Summary of recommendations from the National Institute for Occupational Safety and Health Fire Fighter Fatality Investigation and Prevention Program, 2006-2014.

INTRODUCTION: The NIOSH Fire Fighter Fatality Investigation and Prevention Program (FFFIPP) conducts independent investigations of selected fire fighter line-of-duty deaths (LODD) and offers recommendations to prevent similar deaths. The purpose of the current study was to provide information on more recent FFFIPP recommendations and to determine if recommendations have changed over time. METHODS: Fatality investigations completed from 2006 to 2014 were selected for this study with recommendations being assigned into twelve major categories when possible. The most frequently occurring recommendations were then rank ordered overall and then by medical and traumatic fire fighter LODD. RESULTS: There were 1,067 total recommendations made in the published fire fighter investigative reports for both medical and trauma-related fire fighter fatalities for the period 2006-2014. Of these, 784 (73%) could be placed within one of the 12 categories noted previously. The top 10 recommendation categories overall were: 1. Medical screening, 2. Fitness and wellness program, 3. Training, 4. Medical clearance, 5. Standard Operating Procedures/Standard Operating Guidelines (SOPs/SOGs), 6. Incident command, 7. Strategy and tactics, 8. Communications, 9. Personal protective equipment and 10. Staffing. CONCLUSIONS: The leading recommendations from the NIOSH FFFIPP medical investigations between 2006 and 2014 did not change compared to those made between 1998 and 2005, with the exception of the addition of "medical clearance for duty". There were changes for the traumatic injury leading recommendations for 2006-2014, with the major change being "training", which was the leading FFFIPP recommendation for traumatic injuries for this time period. Practical applications: The intent of the FFFIPP is to influence fire departments and fire fighters to critically assess and evaluate situations/circumstances similar to those identified by NIOSH investigations and implement the recommendations offered to prevent additional fire fighter fatalities.

Origin and domestication of papaya Yh chromosome.

Sex in papaya is controlled by a pair of nascent sex chromosomes. Females are XX, and two slightly different Y chromosomes distinguish males (XY) and hermaphrodites (XY(h)). The hermaphrodite-specific region of the Y(h) chromosome (HSY) and its X chromosome counterpart were sequenced and analyzed previously. We now report the sequence of the entire male-specific region of the Y (MSY). We used a BAC-by-BAC approach to sequence the MSY and resequence the Y regions of 24 wild males and the Y(h) regions of 12 cultivated hermaphrodites. The MSY and HSY regions have highly similar gene content and structure, and only 0.4% sequence divergence. The MSY sequences from wild males include three distinct haplotypes, associated with the populations' geographic locations, but gene flow is detected for other genomic regions. The Y(h) sequence is highly similar to one Y haplotype (MSY3) found only in wild dioecious populations from the north Pacific region of Costa Rica. The low MSY3-Y(h) divergence supports the hypothesis that hermaphrodite papaya is a product of human domestication. We estimate that Y(h) arose only ∼ 4000 yr ago, well after crop plant domestication in Mesoamerica >6200 yr ago but coinciding with the rise of the Maya civilization. The Y(h) chromosome has lower nucleotide diversity than the Y, or the genome regions that are not fully sex-linked, consistent with a domestication bottleneck. The identification of the ancestral MSY3 haplotype will expedite investigation of the mutation leading to the domestication of the hermaphrodite Y(h) chromosome. In turn, this mutation should identify the gene that was affected by the carpel-suppressing mutation that was involved in the evolution of males.

An integrated cytogenetic and physical map reveals unevenly distributed recombination spots along the papaya sex chromosomes.

Papaya is a model system for the study of sex chromosome evolution in plants. However, the cytological structures of the papaya chromosomes remain largely unknown and chromosomal features have not been linked with any genetic or genomic data. We constructed a cytogenetic map of the papaya sex chromosome (chromosome 1) by hybridizing 16 microsatellite markers and 2 cytological feature-associated markers on pachytene chromosomes using fluorescence in situ hybridization (FISH). Except for three markers, the order of the markers was concordant to that of marker loci along the linkage map. This discrepancy was likely caused by skewed segregation in the highly heterochromatic or centromeric regions. The papaya sex chromosome is largely euchromatic, its heterochromatin spans about 15 % of the Y chromosome and is mostly restricted to the centromeric and pericentromeric regions. Analysis of the recombination frequency along the papaya sex chromosome revealed a complete suppression of recombination in the centromere and pericentromere region and 60 % higher recombination rate in the long arm than in the short arm. The uneven distribution of recombination events might be caused by differences in sequence composition. Sequence analysis of 18 scaffolds in total length of 15 Mb revealed higher gene density towards the telomeres and lower gene density towards the centromere, and a relatively higher gene density in the long arm than in the short arm. In an opposite trend, the centromeric and pericentromeric region contained the highest repetitive sequences and the long arm showed the lowest repetitive sequences. This cytogenetic map provides essential information for evolutionary study of sex chromosomes in Caricaceae and will facilitate the analysis of papaya sex chromosomes.

Rapid divergence and expansion of the X chromosome in papaya.

X chromosomes have long been thought to conserve the structure and gene content of the ancestral autosome from which the sex chromosomes evolved. We compared the recently evolved papaya sex chromosomes with a homologous autosome of a close relative, the monoecious Vasconcellea monoica, to infer changes since recombination stopped between the papaya sex chromosomes. We sequenced 12 V. monoica bacterial artificial chromosomes, 11 corresponding to the papaya X-specific region, and 1 to a papaya autosomal region. The combined V. monoica X-orthologous sequences are much shorter (1.10 Mb) than the corresponding papaya region (2.56 Mb). Given that the V. monoica genome is 41% larger than that of papaya, this finding suggests considerable expansion of the papaya X; expansion is supported by a higher repetitive sequence content of the X compared with the papaya autosomal sequence. The alignable regions include 27 transcript-encoding sequences, only 6 of which are functional X/V. monoica gene pairs. Sequence divergence from the V. monoica orthologs is almost identical for papaya X and Y alleles; the Carica-Vasconcellea split therefore occurred before the papaya sex chromosomes stopped recombining, making V. monoica a suitable outgroup for inferring changes in papaya sex chromosomes. The papaya X and the hermaphrodite-specific region of the Y(h) chromosome and V. monoica have all gained and lost genes, including a surprising amount of changes in the X.

Sequencing papaya X and Yh chromosomes reveals molecular basis of incipient sex chromosome evolution.

Sex determination in papaya is controlled by a recently evolved XY chromosome pair, with two slightly different Y chromosomes controlling the development of males (Y) and hermaphrodites (Y(h)). To study the events of early sex chromosome evolution, we sequenced the hermaphrodite-specific region of the Y(h) chromosome (HSY) and its X counterpart, yielding an 8.1-megabase (Mb) HSY pseudomolecule, and a 3.5-Mb sequence for the corresponding X region. The HSY is larger than the X region, mostly due to retrotransposon insertions. The papaya HSY differs from the X region by two large-scale inversions, the first of which likely caused the recombination suppression between the X and Y(h) chromosomes, followed by numerous additional chromosomal rearrangements. Altogether, including the X and/or HSY regions, 124 transcription units were annotated, including 50 functional pairs present in both the X and HSY. Ten HSY genes had functional homologs elsewhere in the papaya autosomal regions, suggesting movement of genes onto the HSY, whereas the X region had none. Sequence divergence between 70 transcripts shared by the X and HSY revealed two evolutionary strata in the X chromosome, corresponding to the two inversions on the HSY, the older of which evolved about 7.0 million years ago. Gene content differences between the HSY and X are greatest in the older stratum, whereas the gene content and order of the collinear regions are identical. Our findings support theoretical models of early sex chromosome evolution.

Construction of physical maps for the sex-specific regions of papaya sex chromosomes.

BACKGROUND: Papaya is a major fruit crop in tropical and subtropical regions worldwide. It is trioecious with three sex forms: male, female, and hermaphrodite. Sex determination is controlled by a pair of nascent sex chromosomes with two slightly different Y chromosomes, Y for male and Yh for hermaphrodite. The sex chromosome genotypes are XY (male), XYh (hermaphrodite), and XX (female). The papaya hermaphrodite-specific Yh chromosome region (HSY) is pericentromeric and heterochromatic. Physical mapping of HSY and its X counterpart is essential for sequencing these regions and uncovering the early events of sex chromosome evolution and to identify the sex determination genes for crop improvement. RESULTS: A reiterate chromosome walking strategy was applied to construct the two physical maps with three bacterial artificial chromosome (BAC) libraries. The HSY physical map consists of 68 overlapped BACs on the minimum tiling path, and covers all four HSY-specific Knobs. One gap remained in the region of Knob 1, the only knob structure shared between HSY and X, due to the lack of HSY-specific sequences. This gap was filled on the physical map of the HSY corresponding region in the X chromosome. The X physical map consists of 44 BACs on the minimum tiling path with one gap remaining in the middle, due to the nature of highly repetitive sequences. This gap was filled on the HSY physical map. The borders of the non-recombining HSY were defined genetically by fine mapping using 1460 F2 individuals. The genetically defined HSY spanned approximately 8.5 Mb, whereas its X counterpart extended about 5.4 Mb including a 900 Kb region containing the Knob 1 shared by the HSY and X. The 8.5 Mb HSY corresponds to 4.5 Mb of its X counterpart, showing 4 Mb (89%) DNA sequence expansion. CONCLUSION: The 89% increase of DNA sequence in HSY indicates rapid expansion of the Yh chromosome after genetic recombination was suppressed 2-3 million years ago. The genetically defined borders coincide with the common BACs on the minimum tiling paths of HSY and X. The minimum tiling paths of HSY and its X counterpart are being used for sequencing these X and Yh-specific regions.

Fatal and nonfatal injuries among emergency medical technicians and paramedics.

BACKGROUND: Emergency medical technicians (EMTs) and paramedics serve as primary providers of urgent medical care and are integral components in disaster response. They are at risk for fatal and nonfatal injuries during these activities. OBJECTIVES: To describe fatal and nonfatal injuries occurring to EMTs and paramedics. METHODS: We analyzed data from the Bureau of Labor Statistics (BLS) Census of Fatal Occupational Injuries (CFOI) and the occupational supplement to the National Electronic Injury Surveillance System (NEISS-Work) for the period 2003-2007. RESULTS: We identified 99,400 (95% confidence interval [CI], 71,700, 127,100) nonfatal injuries treated in emergency departments and 65 fatal injuries from the period 2003-2007. Most fatalities were related to motor vehicle incidents (45%) and aircraft crashes (31%). Among compensated EMTs and paramedics, the rate of fatal injuries was 6.3 per 100,000 full-time equivalents. Nonfatal injuries were primarily associated with stress on some part of the body from motion or overexertion (33%). Among all nonfatal injuries, the most common diagnosis was sprains and strains (38%). CONCLUSIONS: Emergency medical technicians and paramedics have higher fatal injury rates when compared with all workers. To reduce fatalities, targeted efforts should be made to prevent ground and air transportation incidents. Reducing nonfatal injuries may be accomplished by developing and evaluating interventions to prevent bodily stress and overexertion injuries.

Sugarcane for bioenergy production: an assessment of yield and regulation of sucrose content.

An increasing number of plant scientists, including breeders, agronomists, physiologists and molecular biologists, are working towards the development of new and improved energy crops. Research is increasingly focused on how to design crops specifically for bioenergy production and increased biomass generation for biofuel purposes. The most important biofuel to date is bioethanol produced from sugars (sucrose and starch). Second generation bioethanol is also being targeted for studies to allow the use of the cell wall (lignocellulose) as a source of carbon. If a crop is to be used for bioenergy production, the crop should be high yielding, fast growing, low lignin content and requiring relatively small energy inputs for its growth and harvest. Obtaining high yields in nonprime agricultural land is a key for energy crop development to allow sustainability and avoid competition with food production. Sugarcane is the most efficient bioenergy crop of tropical and subtropical regions, and biotechnological tools for the improvement of this crop are advancing rapidly. We focus this review on the studies of sugarcane genes associated with sucrose content, biomass and cell wall metabolism and the preliminary physiological characterization of cultivars that contrast for sugar and biomass yield.

Cloning of the papaya chromoplast-specific lycopene beta-cyclase, CpCYC-b, controlling fruit flesh color reveals conserved microsynteny and a recombination hot spot.

Carotenoid pigments in fruits are indicative of the ripening process and potential nutritional value. Papaya (Carica papaya) fruit flesh color is caused by the accumulation of lycopene or beta-carotenoids in chromoplasts. It is a distinct feature affecting nutritional composition, fruit quality, shelf life, and consumer preference. To uncover the molecular basis of papaya flesh color, we took map-based cloning and candidate gene approaches using integrated genetic and physical maps. A DNA marker tightly linked to flesh color colocalized on a contig of the physical map with a cDNA probe of the tomato (Solanum lycopersicum) chromoplast-specific lycopene beta-cyclase, CYC-b. Candidate gene sequences were obtained from amplified fragments and verified by sequencing two bacterial artificial chromosomes containing the two alleles. Sequence comparison revealed a 2-bp insertion in the coding region of the recessive red flesh allele resulting in a frame-shift mutation and a premature stop codon. A color complementation test in bacteria confirmed that the papaya CpCYC-b is the gene controlling fruit flesh color. Sequence analysis of wild and cultivated papaya accessions showed the presence of this frame-shift mutation in all red flesh accessions examined. Evaluation of DNA markers near CpCYC-b revealed a recombination hot spot, showing that CpCYC-b is located in a gene-rich region with a recombination rate at 3.7 kb per centimorgan, more than 100-fold higher than the genome average at 400 kb per centimorgan. Conserved microsynteny of the CpCYC-b region is indicated by colinearity of two to four genes between papaya, Arabidopsis (Arabidopsis thaliana), grape (Vitis vinifera), and tomato. Our results enhanced our understanding of papaya flesh color inheritance and generated new tools for papaya improvement.

Enrichment of a papaya high-density genetic map with AFLP markers.

A high-density genetic linkage map of papaya, previously developed using an F2 mapping population derived from the intraspecific cross AU9 x SunUp, was enriched with AFLP markers. The comprehensive genetic map presented here spans 945.2 cM and covers 9 major and 5 minor linkage groups containing 712 SSR, 277 AFLP, and 1 morphological markers. The average marker density for the 9 major linkage groups is 0.9 cM between adjacent markers, and the total number of gaps >5 cM was reduced from 48 to 27 in the current map. AFLPs generated by EcoRI/MseI primer combinations were distributed throughout the 14 linkage groups and resulted in several large locus order rearrangements within the 9 major linkage groups. Integration of AFLP markers provided tighter linkage association between loci, leading to a reduction in map distance on LGs 1, 2, and 4, which were inflated in the previous map, and correction of the marker order on LG8. Suppression of recombination in the male-specific Y region (MSY) of LG1 is further validated by the addition of 27 sex co-segregating AFLP markers. A large region of distorted segregation surrounding the MSY spans 54.4 cM and represents approximately 71% of the linkage group. This comprehensive high-density genetic map provides a framework for mapping quantitative trait loci and for fine mapping as well as for comparative genomic studies of crop plant development and evolution.

A physical map of the papaya genome with integrated genetic map and genome sequence.

BACKGROUND: Papaya is a major fruit crop in tropical and subtropical regions worldwide and has primitive sex chromosomes controlling sex determination in this trioecious species. The papaya genome was recently sequenced because of its agricultural importance, unique biological features, and successful application of transgenic papaya for resistance to papaya ringspot virus. As a part of the genome sequencing project, we constructed a BAC-based physical map using a high information-content fingerprinting approach to assist whole genome shotgun sequence assembly. RESULTS: The physical map consists of 963 contigs, representing 9.4x genome equivalents, and was integrated with the genetic map and genome sequence using BAC end sequences and a sequence-tagged high-density genetic map. The estimated genome coverage of the physical map is about 95.8%, while 72.4% of the genome was aligned to the genetic map. A total of 1,181 high quality overgo (overlapping oligonucleotide) probes representing conserved sequences in Arabidopsis and genetically mapped loci in Brassica were anchored on the physical map, which provides a foundation for comparative genomics in the Brassicales. The integrated genetic and physical map aligned with the genome sequence revealed recombination hotspots as well as regions suppressed for recombination across the genome, particularly on the recently evolved sex chromosomes. Suppression of recombination spread to the adjacent region of the male specific region of the Y chromosome (MSY), and recombination rates were recovered gradually and then exceeded the genome average. Recombination hotspots were observed at about 10 Mb away on both sides of the MSY, showing 7-fold increase compared with the genome wide average, demonstrating the dynamics of recombination of the sex chromosomes. CONCLUSION: A BAC-based physical map of papaya was constructed and integrated with the genetic map and genome sequence. The integrated map facilitated the draft genome assembly, and is a valuable resource for comparative genomics and map-based cloning of agronomically and economically important genes and for sex chromosome research.

The P0 gene of Sugarcane yellow leaf virus encodes an RNA silencing suppressor with unique activities.

The Sugarcane yellow leaf virus (SCYLV) P0, a member of the highly heterologous proteins of poleroviruses, is a suppressor of posttranscriptional gene silencing (PTGS) and has additional activities not seen in other P0 proteins. The P0 protein in previously tested poleroviruses (Beet western yellows virus and Cucurbit aphid-borne yellows virus), suppresses local, but not systemic, PTGS induced by both sense GFP and inverted repeat GF using its F-box-like domain to mediate destabilization of the Argonaute1 protein. We now report that the SCYLV P0 protein not only suppressed local PTGS induced by sense GFP and inverted repeat GF in Nicotiana benthamiana, but also triggered a dosage dependent cell death phenotype in infiltrated leaves and suppressed systemic sense GFP-PTGS. Deletion of the first 15 N-terminal amino acid residues of SCYLV P0 abolished suppression of both local and systemic PTGS and the induction of cell death. In contrast, only systemic PTGS and cell death were lost when the 15 C-terminal amino acid residues were deleted. We conclude that the 15 C-terminal amino acid residue region of SCYLV P0 is necessary for suppressing systemic PTGS and inducing cell death, but is not required for suppression of local PTGS.

Agrobacterium tumefaciens-mediated transformation of taro (Colocasia esculenta (L.) Schott) with a rice chitinase gene for improved tolerance to a fungal pathogen Sclerotium rolfsii.

Taro (Colocasia esculenta) is one of the most important crops in the Pacific Islands, however, taro yields have been declining in Hawaii over the past 30 years partly due to diseases caused by oomycete and fungal pathogens. In this study, an efficient Agrobacterium tumefaciens-mediated transformation method for taro is first reported. In total, approximately 200 pieces (8 g) of embryogenic calluses were infected with the super-virulent A. tumefaciens strain EHA105 harboring the plant transformation plasmid pBI121/ricchi11 that contains the rice chitinase gene ricchi11. The presence and expression of the transgene ricchi11 in six independent transgenic lines was confirmed using polymerase chain reaction (PCR) and reverse transcription-PCR (RT-PCR). Southern blot analysis of the six independent lines indicated that three out of six (50%) had integrated a single copy of the transgene, and the other three lines had two or three copies of the transgene. Compared to the particle bombardment transformation of taro method, which was used in the previous studies, the Agrobacterium-mediated transformation method obtained 43-fold higher transformation efficiency. In addition, these six transgenic lines via Agrobacterium may be more effective for transgene expression as a result of single-copy or low-copy insertion of the transgene than the single line with multiple copies of the transgene via particle bombardment. In a laboratory bioassay, all six transgenic lines exhibited increased tolerance to the fungal pathogen Sclerotium rolfsii, ranging from 42 to 63% reduction in lesion expansion.

B-class MADS-box genes in trioecious papaya: two paleoAP3 paralogs, CpTM6-1 and CpTM6-2, and a PI ortholog CpPI.

In the ABC model of flower development, B function organ-identity genes act in the second and third whorls of the flower to control petal and stamen identity. The trioecious papaya has male, female, and hermaphrodite flowers and is an ideal system for testing the B-class gene expression patterns in trioecious plants. We cloned papaya B-class genes, CpTM6-1, CpTM6-2, and CpPI, using MADS box gene specific degenerate primers followed by cDNA library screening and sequencing of positive clones. While phylogenetic analyses show that CpPI is the ortholog of the Arabidopsis gene PI, the CpTM6-1 and CpTM6-2 loci are representatives of the paralogous TM6 lineage that contain paleoAP3 motifs unlike the euAP3 gene observed in Arabidopsis. These two paralogs appeared to have originated from a tandem duplication occurred approximately 13.4 million year ago (mya) (bootstrap range 13.36 +/- 2.42). In-situ hybridization and RT-PCR showed that the papaya B-class genes were highly expressed in young flowers across all floral organ primordia. As the flower organs developed, all three B-class genes were highly expressed in petals of all three-sex types and in stamens of hermaphrodite and male flowers. CpTM6-1 expressed at low levels in sepals and carpels, whereas CpTM6-2 expressed at a low level in sepals and at a high level in leaves. Our results showed that B-class gene homologs could function as predicted by the ABC model in trioecous flowers but differential expressions of CpTM6-1, and CpTM6-2, and CpPI suggested the diversification of their functions after the duplication events.

Low X/Y divergence in four pairs of papaya sex-linked genes.

Sex chromosomes in flowering plants, in contrast to those in animals, evolved relatively recently and only a few are heteromorphic. The homomorphic sex chromosomes of papaya show features of incipient sex chromosome evolution. We investigated the features of paired X- and Y-specific bacterial artificial chromosomes (BACs), and estimated the time of divergence in four pairs of sex-linked genes. We report the results of a comparative analysis of long contiguous genomic DNA sequences between the X and hermaphrodite Y (Y(h)) chromosomes. Numerous chromosomal rearrangements were detected in the male-specific region of the Y chromosome (MSY), including inversions, deletions, insertions, duplications and translocations, showing the dynamic evolutionary process on the MSY after recombination ceased. DNA sequence expansion was documented in the two regions of the MSY, demonstrating that the cytologically homomorphic sex chromosomes are heteromorphic at the molecular level. Analysis of sequence divergence between four X and Y(h) gene pairs resulted in a estimated age of divergence of between 0.5 and 2.2 million years, supporting a recent origin of the papaya sex chromosomes. Our findings indicate that sex chromosomes did not evolve at the family level in Caricaceae, and reinforce the theory that sex chromosomes evolve at the species level in some lineages.

Construction of a sequence-tagged high-density genetic map of papaya for comparative structural and evolutionary genomics in brassicales.

A high-density genetic map of papaya (Carica papaya L.) was constructed using microsatellite markers derived from BAC end sequences and whole-genome shot gun sequences. Fifty-four F(2) plants derived from varieties AU9 and SunUp were used for linkage mapping. A total of 707 markers, including 706 microsatellite loci and the morphological marker fruit flesh color, were mapped into nine major and three minor linkage groups. The resulting map spanned 1069.9 cM with an average distance of 1.5 cM between adjacent markers. This sequence-based microsatellite map resolved the very large linkage group 2 (LG 2) of the previous high-density map using amplified fragment length polymorphism markers. The nine major LGs of our map represent papaya's haploid nine chromosomes with LG 1 of the sex chromosome being the largest. This map validates the suppression of recombination at the male-specific region of the Y chromosome (MSY) mapped on LG 1 and at potential centromeric regions of other LGs. Segregation distortion was detected in a large region on LG 1 surrounding the MSY region due to the abortion of the YY genotype and in a region of LG6 due to an unknown cause. This high-density sequence-tagged genetic map is being used to integrate genetic and physical maps and to assign genome sequence scaffolds to papaya chromosomes. It provides a framework for comparative structural and evolutional genomic research in the order Brassicales.

Chromosomal location and gene paucity of the male specific region on papaya Y chromosome.

Sex chromosomes in flowering plants evolved recently and many of them remain homomorphic, including those in papaya. We investigated the chromosomal location of papaya's small male specific region of the hermaphrodite Y (Yh) chromosome (MSY) and its genomic features. We conducted chromosome fluorescence in situ hybridization mapping of Yh-specific bacterial artificial chromosomes (BACs) and placed the MSY near the centromere of the papaya Y chromosome. Then we sequenced five MSY BACs to examine the genomic features of this specialized region, which resulted in the largest collection of contiguous genomic DNA sequences of a Y chromosome in flowering plants. Extreme gene paucity was observed in the papaya MSY with no functional gene identified in 715 kb MSY sequences. A high density of retroelements and local sequence duplications were detected in the MSY that is suppressed for recombination. Location of the papaya MSY near the centromere might have provided recombination suppression and fostered paucity of genes in the male specific region of the Y chromosome. Our findings provide critical information for deciphering the sex chromosomes in papaya and reference information for comparative studies of other sex chromosomes in animals and plants.

Sex determination in papaya.

Sex determination is an intriguing system in trioecious papaya. Over the past seven decades various hypotheses, based on the knowledge and information available at the time, have been proposed to explain the genetics of the papaya's sex determination. These include a single gene with three alleles, a group of closely linked genes, a genic balance of sex chromosome over autosomes, classical XY chromosomes, and regulatory elements of the flower development pathway. Recent advancements in genomic technology make it possible to characterize the genomic region involved in sex determination at the molecular level. High density linkage mapping validated the hypothesis that predicted recombination suppression at the sex determination locus. Physical mapping and sample sequencing of the non-recombination region led to the conclusion that sex determination is controlled by a pair of primitive sex chromosomes with a small male-specific region (MSY) of the Y chromosome. We now postulate that two sex determination genes control the sex determination pathway. One, a feminizing or stamen suppressor gene, causes stamen abortion before or at flower inception while the other, a masculinizing or carpel suppressor gene, causes carpel abortion at a later flower developmental stage. Detailed physical mapping is beginning to reveal structural details about the sex determination region and sequencing is expected to uncover candidate sex determining genes. Cloning of the sex determination genes and understanding the sex determination process could have profound application in papaya production.

Genomics of sex chromosomes.

Sex chromosomes in plants and animals are distinctive, not only because of their gender-determining role but also for genomic features that reflect their evolutionary history. The genomic sequences in the ancient sex chromosomes of humans and in the incipient sex chromosomes of medaka, stickleback, papaya, and poplar exhibit unusual features as consequences of their evolution. These include the enormous palindrome structure in human MSY, a duplicated genomic fragment that evolved into a Y chromosome in medaka, and a 700 kb extra telomeric sequence of the W chromosome in poplar. Comparative genomic analysis of ancient and incipient sex chromosomes highlights common features that implicate the selection forces that shaped them, even though evolutionary origin, pace, and fate vary widely among individual sex-determining systems.

Ectopic expression of Dahlia merckii defensin DmAMP1 improves papaya resistance to Phytophthora palmivora by reducing pathogen vigor.

Phytophthora spp., some of the more important casual agents of plant diseases, are responsible for heavy economic losses worldwide. Plant defensins have been introduced as transgenes into a range of species to increase host resistance to pathogens to which they were originally susceptible. However, the effectiveness and mechanism of interaction of the defensins with Phytophthora spp. have not been clearly characterized in planta. In this study, we expressed the Dahlia merckii defensin, DmAMP1, in papaya (Carica papaya L.), a plant highly susceptible to a root, stem, and fruit rot disease caused by Phytophthora palmivora. Extracts of total leaf proteins from transformed plants inhibited growth of Phytophthora in vitro and discs cut from the leaves of transformed plants inhibited growth of Phytophthora in a bioassay. Results from our greenhouse inoculation experiments demonstrate that expressing the DmAMP1 gene in papaya plants increased resistance against P. palmivora and that this increased resistance was associated with reduced hyphae growth of P. palmivora at the infection sites. The inhibitory effects of DmAMP1 expression in papaya suggest this approach has good potential to impart transgenic resistance against Phytophthora in papaya.