Chromosome level genome assembly of colored calla lily (Zantedeschia elliottiana).

The colored calla lily is an ornamental floral plant native to southern Africa, belonging to the Zantedeschia genus of the Araceae family. We generated a high-quality chromosome-level genome of the colored calla lily, with a size of 1,154 Mb and a contig N50 of 42 Mb. We anchored 98.5% of the contigs (1,137 Mb) into 16 pseudo-chromosomes, and identified 60.18% of the sequences (694 Mb) as repetitive sequences. Functional annotations were assigned to 95.1% of the predicted protein-coding genes (36,165). Additionally, we annotated 469 miRNAs, 1,652 tRNAs, 10,033 rRNAs, and 1,677 snRNAs. Furthermore, Gypsy-type LTR retrotransposons insertions in the genome are the primary factor causing significant genome size variation in Araceae species. This high-quality genome assembly provides valuable resources for understanding genome size differences within the Araceae family and advancing genomic research on colored calla lily.

First Report of Providencia rettgeri Causing Soft Rot on Calla lily in China.

Calla lily (Zantedeschia hybrida) is widely cultivated as an ornamental plant in China and commonly used as cut flower. Water soaked lesions on the tuber and petiole followed by collapse of entire plant along with foul smell were noticed in a 4-hectare calla lily plantation in the Yanqing District of Beijing, China during August 2022. It was revealed 20%-30% of the plants had these symptoms. Petiole (5 cm) and tuber (5 mm3) samples were collected from 10 plants randomly from fields. The samples were disinfected with 75% ethanol for 5 s, and then rinsed three times with distilled water (DW). Five small pieces for each collected petiole and tuber (about 0.25 cm2 in area) were ground in DW; the suspension was plated on Luria Bertani agar and incubated for 12 h at 28°C. Single colonies were picked and re-streaked three times to purify the bacterial culture. The colonies were creamy, short rod-shaped, gray translucent, and with shiny texture. Gram staining revealed red color, confirming it as Gram-negative bacteria (Werkman et al. 1932). For molecular analysis, DNA was directly extracted from single colony using FastPure Bacteria DNA Isolation Mini Kit (Vazyme Biotech Co., Ltd. Nanjing, China). Four gene-specific markers (16S rRNA, dnaJ, atpD, and ropB) were then amplified using their respective primer pairs (Monciardini et al. 2002). The sequences obtained from four strains, namely ZAPR22R, ZAPR22L, ZAPR22P and ZAPR22S, were submitted after editing to GenBank with accession numbers OP740771.1-OP740774.1 for 16S rRNA, OP759518.1-OP759521.1 for atpD, OP759514.1-OP759517.1 for dnaJ, and OP759510.1-OP759513.1 for ropB genes. All of these gene sequences have the highest BLAST hit to Providencia rettgeri with 94.8% to 99.8% sequence identity (expcept dnaJ, 88.3%) and 96% to 100% of coverage. Phylogenetic tree constructed based on sequences of all four genes using RAxML v8.2.12 (github.com/stamatak/standard-RAxML) showed that the calla lily bacterial strains were clustered with type strain of P. rettgeri). Koch's postulate was performed to confirm the pathogenicity of the bacterial strain ZAPR22R by inoculating petiole base of 20 seedlings of Zantedeschia cv. 'Jingcai Yangguang' with the classical injection procedure. Three sites 1-2cm above the petiole base of individual plant were injected with 100 µl of 108 CFU/ml bacteria, and each was spaced 1 cm apart. All samples were incubated with 16 h of light and 8 h of darkness in a culture chamber at 70-80% relative humidity and 30℃. Soft rot symptoms were developed at the inoculated site after twenty days of inoculation, while no symptoms appeared in the controls. Bacteria reisolated from the inoculated tissues had similar phenotypes and identical molecular characteristics as the original isolate. To our knowledge, this is the first report of the occurrence of P. rettgeri on calla lily in China. P. rettgeri was described as a rhizobacterium that promotes the growth of vegetable crops and lichens from Brazil (Cavalcante da Silva et al. 2020; Swamy et al. 2016). In contrast, it was recently identified as the pathogenic bacterium which cause brown slime flux on Populus tomentosa, a Chinese deciduous tree (Zhou et al. 2020). In the present study, the soft rot was identified as a major disease affecting the growth of calla lily and posing a great threat to commercial calla lily industry. It also provides insights that more studies should be performed on the epidemiology of the disease in different parts of China to establish effective disease management strategies.

Develop a preliminary core germplasm with the novel polymorphism EST-SSRs derived from three transcriptomes of colored calla lily (Zantedeschia hybrida).

The development of high-throughput sequencing technology has made it possible to develop molecular markers such as EST-SSR from transcriptome sequences in non-model plants such as bulbous flowers. However, the EST-SSR markers that have been developed are weakly validated and low polymorphic due to the short read size and poor quality of the assembled sequences. This study therefore used the CandiSSR pipeline to identify 550 potential polymorphic SSR loci among 487 homologous unigenes based on the transcriptomic sequences of three varieties of colored calla lily, and 460 of these loci with appropriate flanking sequences were suitable for primer pairs design. A further validation with 200 randomly selected EST-SSRs demonstrated an increase of more than 30% and 100% in amplification validity and polymorphism, respectively, in comparison with our previous study. In addition, since most of the current varieties of colored calla lily are hybridized from a few species, which have low genetic diversity, we subsequently identified primary core germplasm for 160 colored calla lily accessions using the aforementioned 40 polymorphic EST-SSRs. It was concluded that the core germplasm containing 42 accessions derived from the M strategy incorporated into the software Power Core was the most representative of all 160 original germplasm, as evidenced by the preservation of 100% of the EST-SSR variation, with a higher level of genetic diversity and heterogeneity (Nei = 0.40, I = 0.66, PIC = 0.43). This study provides a practical example of polymorphism EST-SSR markers developed from multiple transcriptomes for non-model plants. A future breeding program for colored calla lily will also benefit from the core germplasm defined by those molecular markers.

Establishment of an efficient regeneration and Agrobacterium transformation system in mature embryos of calla lily (Zantedeschia spp.).

Calla lily (Zantedeschia spp.) have great aesthetic value due to their spathe-like appearance and richness of coloration. However, embryonic callus regeneration is absent from its current regeneration mechanism. As a result, constructing an adequate and stable genetic transformation system is hampered, severely hindering breeding efforts. In this research, the callus induction effectiveness of calla lily seed embryos of various maturities was evaluated. The findings indicated that mature seed embryos were more suitable for in vitro regeneration. Using orthogonal design experiments, the primary elements influencing in vitro regeneration, such as plant growth regulators, genotypes, and nanoscale materials, which was emergent uses for in vitro regeneration, were investigated. The findings indicated that MS supplemented with 6-BA 2 mg/L and NAA 0.1 mg/L was the optimal medium for callus induction (CIM); the germination medium (GM) was MS supplemented with 6-BA 2 mg/L NAA 0.2 mg/L and 1 mg/L CNTs, and the rooting medium (RM) was MS supplemented with 6-BA 2 mg/L NAA 0.7 mg/L and 2 mg/L CNTs. This allowed us to verify, in principle, that the Agrobacterium tumefaciens-mediated genetic transformation system operates under optimal circumstances using the GUS reporter gene. Here, we developed a seed embryo-based genetic transformation regeneration system, which set the stage for future attempts to create new calla lily varieties.

A multifaceted comparison between the fruit-abscission and fruit-retention cultivars in ornamental crabapple.

The ornamental crabapple is a multipurpose landscaping tree that bears brilliant fruit throughout the winter. However, whether or not its fruit persists after maturation is specifically correlated to cultivar characteristics. In this work, we screened two different types that display fruit-retention ("Donald Wyman," "Red Jewel," and "Sugar Tyme") and fruit-abscission ("Radiant" and "Flame") in Northern China across the whole winter using multi-year successional records. Fruit-abscission was determined predominantly by the abscission zone established at the base of the pedicel, regardless of fruit size and pedicel length, according to the results of the comparative research. The primary physiological rationale was the accumulation of hydrolases activity (pectinesterase, cellulase, polygalacturonase, and ß-glucosidase). Comparative transcriptomics further identified a number of upregulated DEGs involved in the synthesis pathways of canonical phytohormones, such as ethylene, jasmonic acid, abscisic acid, and cytokinin, as well as 12 transcription factors linked in downstream signaling in fruit-abscission cultivars. Finally, a model incorporating multi-layered modulation was proposed for the fruit abscission of ornamental crabapple. This study will serve as the foundation for the development of fruit-viewing crabapples that have an extended ornamental lifetime.

Ecological adaptations influence the susceptibility of plants in the genus Zantedeschia to soft rot Pectobacterium spp.

Soft rot disease caused by Pectobacterium spp. is responsible for severe agricultural losses in potato, vegetables, and ornamentals. The genus Zantedeschia includes two botanical groups of tuberous ornamental flowers that are highly susceptible to the disease. Previous studies revealed that Z. aethiopica, a member of the section Zantedeschia, is significantly more resistant to Pectobacterium spp. than members of the same genus that belong to the section Aestivae. During early infection, we found different patterns of bacterial colonization on leaves of hosts belonging to the different sections. Similar patterns of bacterial colonization were observed on polydimethylsiloxane (PDMS) artificial inert replicas of leaf surfaces. The replicas confirmed the physical effect of leaf texture, in addition to a biochemical plant-bacterium interaction. The differential patterns may be associated with the greater roughness of the abaxial leaf surfaces of Aestivae group that have evolutionarily adapted to mountainous environments, as compared to Zantedeschia group species that have adapted to warm, marshy environments. Transverse leaf sections also revealed compact aerenchyma and reduced the total volume of leaf tissue air spaces in Aestivae members. Finally, an analysis of defense marker genes revealed differential expression patterns in response to infection, with significantly higher levels of lipoxygenase 2 (lox2) and phenylalanine ammonia lyase (pal) observed in the more resistant Z. aethiopica, suggesting greater activation of induced systemic resistance (ISR) mechanisms in this group. The use of Zantedeschia as a model plant sheds light on how natural ecological adaptations may underlay resistance to bacterial soft rot in cultivated agricultural environments.

Transcriptome Profiling of Ornithogalum dubium Leaves and Flowers to Identify Key Carotenoid Genes for CRISPR Gene Editing.

Ornithogalum dubium is a popular ornamental monocot native to South Africa with flower colors ranging from pure white to deep orange. Gene editing based on the CRISPR/Cas9 system has recently been shown to hold potential for color improvement in ornamental flower crops. To apply this approach to Ornithogalum color manipulation, genomic or transcriptomic data must first be collected. Here, cDNA libraries of O. dubium leaves and flowers were constructed and sequenced using the Illumina HiSeq 2500. Over 155 million 100-bp paired-end reads were assembled into a transcriptome database of 360,689 contigs, of which 18,660 contigs were differentially expressed between leaves and flowers. Carotenoids are the main pigment imparting spectrum of orange hues to O. dubium flowers. By querying our database, we identified a total of 16 unique transcripts (unigenes) predicted to be involved in the carotenoid biosynthesis pathway of Ornithogalum. Combining carotenoid profiles, we further inferred several key unigenes responsible for floral coloration and accumulation in O. dubium, of which the gene LCYB/comp146645_c0 was found as a suitable target to generate potentially red flower varieties of O. dubium. Our research thus provides a framework for the application of CRISPR/Cas9 technology to improve this ornamental crop.

Author Correction: Revealing the complex genetic structure of cultivated amaryllis (Hippeastrum hybridum) using transcriptome-derived microsatellite markers.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

An improved method for high-temperature induced embryo sac chromosome doubling in Populus simonii Carr. × P. nigra var. italica (Moench.) Kochne, an interspecific hybrid of Tacamahaca and Aigeiros poplars.

Chromosome doubling is considered an important technique in poplar breeding, with many triploid clones being artificially induced and selected for promotion in the north and northeast of China because of their outstanding traits in vegetative growth and environmental adaption. In this study, the triploid yield of Populus simonii Carr × P. nigra var. italica (Moench.) Kochne was 23.41%, which exceeded the yield attained in our previous studies due to the use of an optimized method of chromosome doubling in the embryo sac at a high temperature. The development of the embryo sac after the pollination of this hybrid was investigated to determine the induction period. Ploidy of seedlings was identified by flow cytometry after initial filtering using the chloroplast counting method. Eleven triploids and one tetraploid were ultimately obtained, and the optimal operating conditions were exposure of female catkins to 41 °C for 2 h at 66 h after pollination (HAP). This study identified an efficient method of chromosome doubling in P. simonii × P. nigra var. italica and provided several polyploids for Populus polyploid breeding programs and subsequent studies.

Revealing the complex genetic structure of cultivated amaryllis (Hippeastrum hybridum) using transcriptome-derived microsatellite markers.

Although amaryllis (Hippeastrum hybridum) plants are commonly used in physiological and ecological research, the extent of their genomic and genetic resources remains limited. The development of molecular markers is therefore of great importance to accelerate genetic improvements in Hippeastrum species. In this study, a total of 269 unique genes were defined that might regulate the flower spathe development of amaryllis. In addition, 2000 simple sequence repeats (SSRs) were detected based on 171,462 de novo assembled unigenes from transcriptome data, and 66,4091 single nucleotide polymorphisms (SNPs) were also detected as putative molecular markers. Twenty-one SSR markers were screened to evaluate the genetic diversity and population structure of 104 amaryllis accessions. A total of 98 SSR loci were amplified for all accessions. The results reveal that Nei's gene diversity (H) values of these markers ranged between 0.055 and 0.394, whereas the average values of Shannon's Information index (I) ranged between 0.172 and 0.567. Genetic tree analysis further demonstrates that all accessions can be grouped into three main clusters, which can be further divided into two subgroups. STRUCTURE-based analysis revealed that the highest ΔK values were observed when K = 5, K = 6, K = 7 and K = 8. The results of this study enable large-scale transcriptomics and classification of Hippeastrum genetic polymorphisms and will be useful in the future for resource conservation and production.

Assessing Genetic Diversity and Population Differentiation of Colored Calla Lily (Zantedeschia Hybrid) for an Efficient Breeding Program.

Plastome-genome incompatibility (PGI) is prevalent in several plants including the Zantedeschia species, a worldwide commercial flower crop native to South Africa. Generally, hybrids suffering from PGI appear less vigorous and more susceptible than normal plants. Previous reports revealed that the PGI level in interspecific hybrids is correlated with the relatedness of the parental species in the genus Zantedeschia. To provide a basis for utilizing and improving resources in breeding programs, a total of 117 accessions of colored calla lily (Zantedeschia hybrid), collected from New Zealand, the Netherlands and the United States, were genotyped using 31 transferable expressed sequence tags-simple sequence repeats (EST-SSR) markers from the white calla lily (Zantedeschia aethiopica). A moderately high level of genetic diversity was observed, with 111 alleles in total, an observed/expected heterozygosity (Ho/He) of 0.453/0.478, and polymorphism information content (PIC) of 0.26. Genetic distance and STRUCTURE-based analysis further clustered all accessions into four subgroups (G-Ia, G-Ib, G-IIa and G-IIb), which mostly consisted of Zantedeschia pentlandii, Zantedeschia elliotiana, Zantedeschia albomaculata and Zantedeschia rehmannii, respectively. Significant genetic differentiation was observed between all inferred subgroup pairs, with the Fst ranging from 0.142 to 0.281. Finally, the accessions assigned into G-IIb (Z. rehmannii) were recommended as top priority parents in efficient Zantedeschia breeding program designs.

Inducing triploids and tetraploids with high temperatures in Populus sect. Tacamahaca.

KEY MESSAGE: This study is the first to report that triploids and tetraploids have been successfully produced through embryo sac and zygotic embryo chromosome doubling with high temperatures in P. simonii Carr. and its hybrid. A new synthetic polyploid induced by hybridization with unreduced gametes and heterozygotic embryo chromosome doubling can effectively combine polyploidy and heterosis, which can provide two major breeding advantages. In Populus, successfully creating and cultivating new polyploid varieties have economic and ecological production value. This was the first successful study in which embryo sac and zygotic embryo chromosome doubling was induced using high temperatures to produce triploids and tetraploids in Populus simonii Carr. and its hybrid, P. simonii × P. nigra var. Italica, of Populus sect. Tacamahaca. The relationship between flower bud morphological characteristics (time after pollination) and female meiotic stage (embryo sac and zygotic embryo development) was established to guide the induction treatment period. In the resulting progeny, 37 triploids and 12 tetraploids were obtained and identified using flow cytometry. The optimal temperatures for embryo sac and zygotic embryo chromosome doubling were 38 and 41 °C, respectively. Cytogenetic analysis revealed that 66-72 h after pollination (HAP), a period characterized by a high proportion of one-nucleate and two-nucleate embryo sacs, was the optimal period for embryo sac chromosome doubling. For zygotic embryo chromosome doubling, 168 HAP was the optimal induction period, as there was a high proportion of two-cell and four-cell proembryos. The results indicate that inducing embryo sac and zygotic embryo chromosome doubling is an ideal method for producing polyploids. The methods for inducing polyploids and for evaluating ploidy and offspring with different ploidies and heterozygosity in this study will be useful for genetic research and Populus breeding programmes.

Transcriptome analysis of colored calla lily (Zantedeschia rehmannii Engl.) by Illumina sequencing: de novo assembly, annotation and EST-SSR marker development.

Colored calla lily is the short name for the species or hybrids in section Aestivae of genus Zantedeschia. It is currently one of the most popular flower plants in the world due to its beautiful flower spathe and long postharvest life. However, little genomic information and few molecular markers are available for its genetic improvement. Here, de novo transcriptome sequencing was performed to produce large transcript sequences for Z. rehmannii cv. 'Rehmannii' using an Illumina HiSeq 2000 instrument. More than 59.9 million cDNA sequence reads were obtained and assembled into 39,298 unigenes with an average length of 1,038 bp. Among these, 21,077 unigenes showed significant similarity to protein sequences in the non-redundant protein database (Nr) and in the Swiss-Prot, Gene Ontology (GO), Cluster of Orthologous Group (COG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. Moreover, a total of 117 unique transcripts were then defined that might regulate the flower spathe development of colored calla lily. Additionally, 9,933 simple sequence repeats (SSRs) and 7,162 single nucleotide polymorphisms (SNPs) were identified as putative molecular markers. High-quality primers for 200 SSR loci were designed and selected, of which 58 amplified reproducible amplicons were polymorphic among 21 accessions of colored calla lily. The sequence information and molecular markers in the present study will provide valuable resources for genetic diversity analysis, germplasm characterization and marker-assisted selection in the genus Zantedeschia.

The genetic regulatory network centered on Pto-Wuschela and its targets involved in wood formation revealed by association studies.

Transcription factors (TFs) regulate gene expression and can strongly affect phenotypes. However, few studies have examined TF variants and TF interactions with their targets in plants. Here, we used genetic association in 435 unrelated individuals of Populus tomentosa to explore the variants in Pto-Wuschela and its targets to decipher the genetic regulatory network of Pto-Wuschela. Our bioinformatics and co-expression analysis identified 53 genes with the motif TCACGTGA as putative targets of Pto-Wuschela. Single-marker association analysis showed that Pto-Wuschela was associated with wood properties, which is in agreement with the observation that it has higher expression in stem vascular tissues in Populus. Also, SNPs in the 53 targets were associated with growth or wood properties under additive or dominance effects, suggesting these genes and Pto-Wuschela may act in the same genetic pathways that affect variation in these quantitative traits. Epistasis analysis indicated that 75.5% of these genes directly or indirectly interacted Pto-Wuschela, revealing the coordinated genetic regulatory network formed by Pto-Wuschela and its targets. Thus, our study provides an alternative method for dissection of the interactions between a TF and its targets, which will strength our understanding of the regulatory roles of TFs in complex traits in plants.

Development and Characterization of Novel EST-SSRs from Larix gmelinii and Their Cross-Species Transferability.

A set of 899 L. gmelinii expression sequence tags (ESTs), available at the National Center of Biotechnology Information (NCBI), was employed to address the feasibility on development of simple sequence repeat (SSR) markers for Larch species. Totally, 634 non-redundant unigenes including 145 contigs and 489 singletons were finally identified and mainly involved in biosynthetic, metabolic processes and response to stress according to BLASTX results, gene ontology (GO) categories and Kyoto Encyclopedia of Genes and Genomes (KEGG) maps. Approximately 11.7% (74) unigenes contained 90 candidate SSRs, which were mainly trinucleotides (29, 32.2%) and dinucleotides (26, 28.9%). A relatively high frequency of SSRs was respectively found in the Open Reading Frame (ORF, about 54.4%) and 5'-untranslated region (5'-UTR, 31.2%), while a low frequency was observed in the 3'-untranslated region (3'-UTR, about 14.4%). Of the 45 novel EST-SSRs markers, nine were found to be polymorphic at two L. gmelinii populations. The number of alleles per locus (Na) ranged from two to four, and the observed (Ho) and expected (He) heterozygosity values were 0.200-0.733 and 0.408-0.604, respectively. The inbreeding coefficients (FIS) for all loci were more than zero except Lg41. Most of these 9EST-SSR markers were transferable to its related species L. kaempferi, L. principis-rupprechtii and L. olgensis. These novel EST-SSRs will be useful for further research on comparative genomics, genetic resources conservation and molecular breeding in larch trees.

Association mapping for morphological and physiological traits in Populus simonii.

BACKGROUND: To optimize marker-assisted selection programs, knowledge of the genetic architecture of phenotypic traits is very important for breeders. Generally, most phenotypes, e.g. morphological and physiological traits, are quantitatively inherited, and thus detection of the genes underlying variation for these traits is difficult. Association mapping based on linkage disequilibrium has recently become a powerful approach to map genes or quantitative trait loci (QTL) in plants. RESULTS: In this study, association analysis using 20 simple sequence repeat (SSR) markers was performed to detect the marker loci linked to 13 morphological traits and 10 physiological traits in a wild P. simonii population that consisted of 528 individuals sampled from 16 sites along the Yellow River in China. Based on a model controlling for both population structure (Q) and relative kinship (K), three SSR markers (GCPM_616-1 in 31.2 Mb on LG I, GCPM_4055-2 in 5.7 Mb on LG XV, and GCPM_3142 of unknown location) were identified for seven traits. GCPM_616-1 was associated with five morphological traits (R2 = 5.14-10.09%), whereas GCPM_3142 (15.03%) and GCPM_4055-2 (13.26%) were associated with one morphological trait and one physiological trait, respectively. CONCLUSIONS: The results suggest that this wild population is suitable for association mapping and the identified markers will be suitable for marker-assisted selection breeding or detection of target genes or QTL in the near future.

Identification and characterization of 43 novel polymorphic EST-SSR markers for arum lily, Zantedeschia aethiopica (Araceae).

PREMISE OF THE STUDY: A new set of microsatellite or simple sequence repeat (SSR) markers from expressed sequence tags (ESTs) was developed for arum lily (Zantedeschia aethiopica), which is one of the most iconic and widely recognized ornamental plants in the world. • METHODS AND RESULTS: Using 2175 unigenes derived from 4283 random ESTs in arum lily, 166 primer pairs were designed and tested for amplification in 24 accessions from Asia, Europe, and Africa. A total of 43 loci were polymorphic, with the number of alleles per locus ranging from two to 10. The observed heterozygosity, expected heterozygosity, and polymorphism information content ranged from 0.2313 to 0.8480, 0.3034 to 0.8648, and 0.1015 to 0.7364, respectively. • CONCLUSIONS: These novel polymorphic EST-SSR markers will facilitate future studies of genetic variation and molecular-assisted breeding systems in arum lily.

Genetic diversity and population structure of Chinese White poplar (Populus tomentosa) revealed by SSR markers.

An understanding of allelic diversity and population structure is important in developing association studies and constructing core collections for tree breeding. We examined population genetic differentiation in the native Populus tomentosa by genotyping 460 unrelated individuals using 20 species-specific microsatellite markers. We identified 99 alleles with a mean of 4.95 observed alleles per locus, indicating a moderate level of polymorphism across all individuals. A model-based population structure analysis divided P. tomentosa into 11 subpopulations (K = 11). The pattern of individual assignments into the subsets (K = 3) provided reasonable evidence for treating climatic zones as genetic regions for population genetics. The highest level of genetic variation was found in the southern region (i.e., N = 93, N (P) = 11, H (E) = 0.445, F = -0.102), followed by the northeastern and northwestern regions. Thus, the southern region is probably the center of the current species distribution. No correlation was found between population genetic distance and geographic distance (r = 0.0855, P = 0.3140), indicating that geographical distance was not the principal factor influencing genetic differentiation in P. tomentosa. These data provide a starting point for conserving valuable natural resources and optimizing breeding programs.

Development of 35 microsatellite markers from heat stress transcription factors in Populus simonii (Salicaceae).

PREMISE OF THE STUDY: Microsatellite markers within regulators of heat stress transcription factors were identified in the Populus trichocarpa genome, and then developed for P. simonii to investigate the genetic diversity of germplasm resources and to further identify favorable alleles significantly associated with stress-resistant traits. METHODS AND RESULTS: Thirty-five novel microsatellite markers were identified from genes controlling heat stress transcription factors in P. simonii using a Sanger sequencing protocol. Polymorphisms in 48 individuals from 16 populations of P. simonii revealed that the number of alleles per locus ranged from two to nine with an average of 4.6; the observed heterozygosity and expected heterozygosity per locus varied from 0.143 to 0.857 and from 0.257 to 0.948, respectively. CONCLUSIONS: The new polymorphic markers developed during this study will facilitate the construction of genetic linkage maps and will aid in marker-assisted breeding of a new germplasm with desirable abiotic stress resistance in Populus species.