As the main byproduct of cotton fiber, the cotton seed yields about 1.6 times that of fiber, with its oil rich in unsaturated fatty acids, mainly linoleic acid. It is desirable for breeders to increase the oil content of cottonseed without affecting the yield and quality of cotton fiber. In this study, a seed-specific promoter- (alpha-globulin gene promoter-) driven GhDGAT1 overexpression vector (P_αGlob) was constructed and used to transform an upland cotton line YZ1 (Gossypium hirsutum). Overexpression of the cotton gene GhDGAT1 in cotton seeds increased its total oil content from 4.7% to 13.9% in different transgenic lines and different generations. With the increase of oil content, the composition and contents of the main fatty acids in cotton seed also changed, as reflected by the contents of the main saturated fatty acids and unsaturated oleic acid. GhDGAT1 could be used to increase oil content and improve oil composition in cottonseed.

Global warming is limiting availability of water resources in arid and semi-arid regions, and so understanding water use efficiency (WUE) is increasingly important for agricultural production in those areas. As China is the largest cotton producing area, the problem of balancing WUE and efficient cotton production is a major issue. In this study, we used a natural population of 517 Upland cotton accessions to conduct a water-controlled trial in south and north of Xinjiang over two years. A total of 18 traits including agronomic traits, fiber yield indices and fiber quality indices, were investigated for broad-sense heritability and coefficient of variation. Appropriate water limitation was found to promote the establishment of favorable agronomic traits in cotton, associated with an increased cotton yield of 8.46% in Xinjiang, at the expense of a certain degree of fiber quality, such as decreased fiber length and an over-higher micronaire value. We detected 33 QTL related to response to water limitation using a drought resistance coefficient (DRC), and 6 QTL were found using a comprehensive indicator of CIDT (comprehensive index of drought tolerance) at the genetic level by integrating resequencing data. Two novel QTL-hotspots including six differentially expressed genes (DEGs) were further identified related to the drought response of cotton. These findings not only suggested a new approach to irrigation of cotton fields in Xinjiang, but also provided abundant genetic evidence for genetic breeders to study drought improvement of crops.

Environmental stresses severely impair cotton production worldwide. To identify the genetic basis of, and molecular markers associated with, environmental stresses such as salt, cold and Verticillium wilt, association mapping of salt-, cold-, and disease-tolerance traits was performed in a population of 503 upland cotton accessions using 179 polymorphic SSR markers and 11,975 array-derived SNP markers. Salt and cold tolerance was evaluated via the relative germination rate (RGR) of the seeds under seven and four environments, respectively. The disease index of Verticillium wilt was investigated for two years in the field in Xinjiang. These three traits showed large variation across environments. A genome-wide association study revealed that 31, 19, and 15 SSR markers were associated with RGR-Salt (the relative germination rates of seeds under salt stress), RGR-Cold (the relative germination rates of seeds under cold stress), and DIV (the disease index of Verticillium wilt), respectively. Six SNPs in seven environments and two SNPs in BLUP (best linear unbiased prediction) results were associated with RGR-Salt, and the phenotypic variance explained ranged from 3.96 to 5.00%. Two SNPs (i02237Gh, i02243Gh) on D01 were concluded to be stable genetic loci associated with RGR-Salt. A total of 223 genes were found in a candidate gene interval (D01, 37771–1942912). Of these four genes, GhPIP3A, GhSAG29, GhTZF4, and GhTZF4a, showed expression changes in sensitive and tolerant genotype accessions under salt stress, and were assigned as candidate genes associated with RGR-Salt. This study revealed the genetic basis of stress resistance in upland cotton and will facilitate stress-resistance breeding in cotton.