Alternative oxidase (AOX) over-expression improves cell expansion and elongation in cotton seedling exposed to cool temperatures.

KEY MESSAGE: Evidence that supports a relation between AOX expression and improvement in plant height, internode length, and total leaf area under cool temperature is shown. Cell expansion and elongation appear to be enhanced when AOX expression was increased. Cotton growth is sensitive to cool temperature during germination and early seedling development. Delayed emergence, seedling damage, and increased risk to disease are common. Late seasonal cool weather is a major factor limiting the consistent production of high-quality cotton lint in West Texas. Alternative oxidase functions in the inner membrane of the mitochondria via an alternative respiration pathway and serves as a multifunctional system for amelioration of abiotic and biotic stresses. Cotton seedling emergence and growth exposed to cool temperatures was examined in plants with enhanced AOX expression. Thirteen T1 seed lines showed 3 to 1 segregation for the T-DNA containing the tobacco AOX1 gene. Two over-expressing, single-copy, homozygous AOX lines (94-20T and 66-6T) and Null line (94-3N) were selected for examination. The transcript levels were ≈ 2 to 6 fold higher in the AOX lines compared to those of the Null line and wild-type in stem, leaf, root and boll tissues. The research examined the hypothesis that transgenic cotton with enhanced AOX expression will have enhanced growth traits under suboptimal cool temperatures. Improved plant height, internode length, plant height and internode length from second node, and total leaf area under cool temperatures were observed in AOX over-expression lines. This may be attributed to improved cell expansion and elongation characteristics in the AOX line.

Toward Coalescing Gene Expression and Function with QTLs of Water-Deficit Stress in Cotton.

Cotton exhibits moderately high vegetative tolerance to water-deficit stress but lint production is restricted by the available rainfed and irrigation capacity. We have described the impact of water-deficit stress on the genetic and metabolic control of fiber quality and production. Here we examine the association of tentative consensus sequences (TCs) derived from various cotton tissues under irrigated and water-limited conditions with stress-responsive QTLs. Three thousand sixteen mapped sequence-tagged-sites were used as anchored targets to examine sequence homology with 15,784 TCs to test the hypothesis that putative stress-responsive genes will map within QTLs associated with stress-related phenotypic variation more frequently than with other genomic regions not associated with these QTLs. Approximately 1,906 of 15,784 TCs were mapped to the consensus map. About 35% of the annotated TCs that mapped within QTL regions were genes involved in an abiotic stress response. By comparison, only 14.5% of the annotated TCs mapped outside these QTLs were classified as abiotic stress genes. A simple binomial probability calculation of this degree of bias being observed if QTL and non-QTL regions are equally likely to contain stress genes was P (x ≥ 85) = 7.99 × 10(-15). These results suggest that the QTL regions have a higher propensity to contain stress genes.

Identification of a single gene for seed coat impermeability in soybean PI 594619.

KEY MESSAGE: Inheritance studies and molecular mapping identified a single dominant gene that conditions seed coat impermeability in soybean PI 594619. High temperatures during seed fill increase the occurrence of soybeans with impermeable seed coat, which is associated with non-uniform and delayed germination and emergence. This can be an issue in soybean production areas with excessively high-temperature environments. The objectives of the present study were to investigate the inheritance of impermeable seed coat under a high-temperature environment in the midsouthern United States and to map the gene(s) that affect this trait in a germplasm line with impermeable seed coat (PI 594619). Crosses were made between PI 594619 and an accession with permeable seed coat at Stoneville, MS in 2008. The parental lines and the segregating populations from reciprocal crosses were grown in Stoneville in 2009. Ninety-nine F2:3 families and parents were also grown at Stoneville, MS in 2011. Seeds were assayed for percent impermeable seed coat using the standard germination test. Genetic analysis of the F2 populations and F2:3 families indicated that seed coat impermeability in PI 594619 is controlled by a single major gene, with impermeable seed coat being dominant to permeable seed coat. Molecular mapping positioned this gene on CHR 2 between markers Sat_202 and Satt459. The designation of Isc (impermeable seed coat) for this single gene has been approved by the Soybean Genetics Committee. Selection of the recessive form (isc) may be important in developing cultivars with permeable seed coat for high-heat production environments. The single-gene nature of impermeable seed coat may also have potential for being utilized in reducing seed damage caused by weathering and mold.

Responses of nitrogen metabolism and seed nutrition to drought stress in soybean genotypes differing in slow-wilting phenotype.

Recent advances in soybean breeding have resulted in genotypes that express the slow-wilting phenotype (trait) under drought stress conditions. The physiological mechanisms of this trait remain unknown due to the complexity of trait × environment interactions. The objective of this research was to investigate nitrogen metabolism and leaf and seed nutrients composition of the slow-wilting soybean genotypes under drought stress conditions. A repeated greenhouse experiment was conducted using check genotypes: NC-Roy (fast wilting), Boggs (intermediate in wilting); and NTCPR94-5157 and N04-9646 (slow-wilting, SLW) genotypes. Plants were either well-watered or drought stressed. Results showed that under well-watered conditions, nitrogen fixation (NF), nitrogen assimilation (NA), and leaf and seed composition differed between genotypes. Under drought stress, NF and NA were higher in NTCPR94-5157 and N04-9646 than in NC-Roy and Boggs. Under severe water stress, however, NA was low in all genotypes. Leaf water potential was significantly lower in checks (-2.00 MPa) than in the SLW genotypes (-1.68 MPa). Leaf and seed concentrations of K, P, Ca, Cu, Na, B were higher in SLW genotypes than in the checks under drought stress conditions. Seed protein, oleic acid, and sugars were higher in SLW genotypes, and oil, linoleic and linolenic acids were lower in SLW genotypes. This research demonstrated that K, P, Ca, Cu, Na, and B may be involved in SLW trait by maintaining homeostasis and osmotic regulation. Maintaining higher leaf water potential in NTCPR94-5157 and N04-9646 under drought stress could be a possible water conservation mechanism to maintain leaf turgor pressure. The increase in osmoregulators such as minerals, raffinose, and stachyose, and oleic acid could be beneficial for soybean breeders in selecting for drought stress tolerance.

Relationship between aflatoxin contamination and physiological responses of corn plants under drought and heat stress.

Increased aflatoxin contamination in corn by the fungus Aspergillus flavus is associated with frequent periods of drought and heat stress during the reproductive stages of the plants. The objective of this study was to evaluate the relationship between aflatoxin contamination and physiological responses of corn plants under drought and heat stress. The study was conducted in Stoneville, MS, USA under irrigated and non-irrigated conditions. Five commercial hybrids, P31G70, P33F87, P32B34, P31B13 and DKC63-42 and two inbred germplasm lines, PI 639055 and PI 489361, were evaluated. The plants were inoculated with Aspergillus flavus (K-54) at mid-silk stage, and aflatoxin contamination was determined on the kernels at harvest. Several physiological measurements which are indicators of stress response were determined. The results suggested that PI 639055, PI 489361 and hybrid DKC63-42 were more sensitive to drought and high temperature stress in the non-irrigated plots and P31G70 was the most tolerant among all the genotypes. Aflatoxin contamination was the highest in DKC63-42 and PI 489361 but significantly lower in P31G70. However, PI 639055, which is an aflatoxin resistant germplasm, had the lowest aflatoxin contamination, even though it was one of the most stressed genotypes. Possible reasons for these differences are discussed. These results suggested that the physiological responses were associated with the level of aflatoxin contamination in all the genotypes, except PI 639055. These and other physiological responses related to stress may help examine differences among corn genotypes in aflatoxin contamination.

Examining the drought stress transcriptome in cotton leaf and root tissue.

Growth, yield, and yield quality of cotton are greatly affected by water-deficit stress. We have identified the genes and associated metabolic pathways involved in the water-deficit stress response in leaf and root. Gene expression profiles were developed for leaf and root tissues subjected to slow-onset water deficit under controlled, glasshouse conditions. The water-deficit stress was characterized by leaf water potential of -23.1 bars for stressed tissue compared to -8.7 bars for fully-irrigated control plants and a corresponding decrease in net carbon assimilation to approximately 60% of the rates seen in the irrigated controls (30.3 ± 4.7 µmol CO(2) m(-2) s(-1) compared to 17.8 ± 5.9 µmol CO(2) m(-2) s(-1)). Profiling experiments revealed 2,106 stress-responsive transcripts, 879 classified as stress-induced, 1,163 stress-repressed, and 64 showed reciprocal expression patterns in root and leaf. The majority of stress-responsive transcripts had tissue-specific expression patterns and only 173 genes showed similar patterns of stress responsive expression in both tissues. A variety of putative metabolic and regulatory pathways were identified using MapMan software and the potential targets for candidate gene selection and ectopic expression to alter these pathways and responses are discussed.