Analysis of Drought Tolerance and Associated Traits in Upland Cotton at the Seedling Stage.

(1) Background: Upland cotton (Gossypium hirsutum L.) is the most important natural fiber worldwide, and it is extensively planted and plentifully used in the textile industry. Major cotton planting regions are frequently affected by abiotic stress, especially drought stress. Drought resistance is a complex, quantitative trait. A genome-wide association study (GWAS) constitutes an efficient method for dissecting the genetic architecture of complex traits. In this study, the drought resistance of a population of 316 upland cotton accessions was studied via GWAS. (2) Methods: GWAS methodology was employed to identify relationships between molecular markers or candidate genes and phenotypes of interest. (3) Results: A total of 8, 3, and 6 SNPs were associated with the euphylla wilting score (EWS), cotyledon wilting score (CWS), and leaf temperature (LT), respectively, based on a general linear model and a factored spectrally transformed linear mixed model. For these traits, 7 QTLs were found, of which 2 each were located on chromosomes A05, A11, and D03, and of which 1 was located on chromosome A01. Importantly, in the candidate regions WRKY70, GhCIPK6, SnRK2.6, and NET1A, which are involved in the response to abscisic acid (ABA), the mitogen-activated protein kinase (MAPK) signaling pathway and the calcium transduction pathway were identified in upland cotton at the seedling stage under drought stress according to annotation information and linkage disequilibrium (LD) block analysis. Moreover, RNA sequencing analysis showed that WRKY70, GhCIPK6, SnRK2.6, and NET1A were induced by drought stress, and the expression of these genes was significantly different between normal and drought stress conditions. (4) Conclusions: The present study should provide some genomic resources for drought resistance in upland cotton. Moreover, the germplasm of the different phenotypes, the detected SNPs and, the potential candidate genes will be helpful for molecular marker-assisted breeding studies about increased drought resistance in upland cotton.

Cloning and characterization of a FLO/LFY ortholog in Gossypium hirsutum L.

KEY MESSAGE: GhLFY was cloned from G. hirsutum L. Its expression, subcellular localization, and function were analyzed, as well as the in vivo regulation of GhLFY by the MADS-box protein SOC1 (GhSOC1). ABSTRACT: Flowering is a very important phase during which plants produce the organs for sexual reproduction. The FLORICAULA/LEAFY (FLO/LFY) homologs play a major role in the initiation of flowering. To understand the mechanism of the transition from the vegetative to reproductive phases in Upland cotton (Gossypium hirsutum L.), we isolated a candidate LFY gene from G. hirsutum L. (GhLFY) that showed a high degree of similarity to other plant homologs of FLO/LFY. qPCR analysis showed that GhLFY was highly expressed in the shoot apex, with substantial upregulation at the third true leaf expansion stage during floral bud differentiation. Subcellular localization studies revealed GhLFY localization in the nucleus. Ectopic expression of the GhLFY coding region in Arabidopsis resulted in early flowering. The expression of the GhLFY coding region under the control of the 35S promoter complemented the lfy-5 mutation in transgenic Arabidopsis lfy-5 mutant plants. Furthermore, a chromatin immunoprecipitation assay revealed that GhLFY may function downstream of GhSOC1 during the initiation of flowering in G. hirsutum L. GhLFY was likely to be regulated by GhSOC1, which binds to the LFY promoter in Arabidopsis. These results suggest that GhLFY is a FLO/LFY ortholog that may be involved in controlling flowering time and floral development.

Comparative proteomics indicates that biosynthesis of pectic precursors is important for cotton fiber and Arabidopsis root hair elongation.

The quality of cotton fiber is determined by its final length and strength, which is a function of primary and secondary cell wall deposition. Using a comparative proteomics approach, we identified 104 proteins from cotton ovules 10 days postanthesis with 93 preferentially accumulated in the wild type and 11 accumulated in the fuzzless-lintless mutant. Bioinformatics analysis indicated that nucleotide sugar metabolism was the most significantly up-regulated biochemical process during fiber elongation. Seven protein spots potentially involved in pectic cell wall polysaccharide biosynthesis were specifically accumulated in wild-type samples at both the protein and transcript levels. Protein and mRNA expression of these genes increased when either ethylene or lignoceric acid (C24:0) was added to the culture medium, suggesting that these compounds may promote fiber elongation by modulating the production of cell wall polymers. Quantitative analysis revealed that fiber primary cell walls contained significantly higher amounts of pectin, whereas more hemicellulose was found in ovule samples. Significant fiber growth was observed when UDP-L-rhamnose, UDP-D-galacturonic acid, or UDP-D-glucuronic acid, all of which were readily incorporated into the pectin fraction of cell wall preparations, was added to the ovule culture medium. The short root hairs of Arabidopsis uer1-1 and gae6-1 mutants were complemented either by genetic transformation of the respective cotton cDNA or by adding a specific pectin precursor to the growth medium. When two pectin precursors, produced by either UDP-4-keto-6-deoxy-D-glucose 3,5-epimerase 4-reductase or by UDP-D-glucose dehydrogenase and UDP-D-glucuronic acid 4-epimerase successively, were used in the chemical complementation assay, wild-type root hair lengths were observed in both cut1 and ein2-5 Arabidopsis seedlings, which showed defects in C24:0 biosynthesis or ethylene signaling, respectively. Our results suggest that ethylene and C24:0 may promote cotton fiber and Arabidopsis root hair growth by activating the pectin biosynthesis network, especially UDP-L-rhamnose and UDP-D-galacturonic acid synthesis.