Cotton is an important natural fiber crop; its seeds are the main oil source. Abiotic stresses cause a significant decline in its production. The WUSCHEL-related Homeobox (WOX) genes have been involved in plant growth, development, and stress responses. However, the functions of WOX genes are less known in cotton. This study identified 39, 40, 21, and 20 WOX genes in Gossypium hirsutum, Gossypium barbadense, Gossypium arboreum, and Gossypium raimondii, respectively. All the WOX genes in four cotton species could be classified into three clades, which is consistent with previous research. The gene structure and conserved domain of all WOX genes were analyzed. The expressions of WOX genes in germinating hypocotyls and callus were characterized, and it was found that most genes were up-regulated. One candidate gene Gh_ A01G127500 was selected to perform the virus-induced gene silencing (VIGS) experiment, and it was found that the growth of the silenced plant (pCLCrVA: GhWOX4_A01) was significantly inhibited compared with the wild type. In the silenced plant, there is an increase in antioxidant activities and a decrease in oxidant activities compared with the control plant. In physiological analysis, the relative electrolyte leakage level and the excised leaf water loss of the infected plant were increased. Still, both the relative leaf water content and the chlorophyll content were decreased. This study proved that WOX genes play important roles in drought stress and callus induction, but more work must be performed to address the molecular functions of WOX genes.

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Background: Cotton stem trichomes and seed fibers are each single celled structures formed by protrusions of epidermal cells, and were found sharing the overlapping molecular mechanism . Compared with fibers, cotton stem trichomes are more easily observed, but the molecular mechanisms underlying their development are still poorly understood.Results: In this study, Gossypium hirsutum (Gh ) and G . barbadense ( Gb ) were found to differ greatly in percentages of varieties/accessions with glabrous stems and in trichome density, length, and number per trichopore. Gh varieties normally had long singular and clustered trichomes, while Gb varieties had short clustered trichomes. Genetic mapping using five F2 populations from crosses between glabrous varieties and those with different types of stem trichomes revealed that much variation among stem trichome phenotypes could be accounted for by different combinations of genes/alleles on Chr.06 and Chr.24. The twenty six F1 generations from crosses between varieties with different types of trichomes had varied phenotypes, further suggesting that the trichomes of tetraploid cotton were controlled by different genes/alleles. Compared to modern varieties, a greater proportion of Gh wild accessions were glabrous or had shorter and denser trichomes; whereas a smaller proportion of Gb primitive accessions had glabrous stems. A close correlation between fuzz fiber number and stem trichome density was observed in both Gh and Gb primitive accessions and modern varieties.Conclusion: Based on these findings, we hypothesize that stem trichomes evolved in parallel with seed fibers during the domestication of cultivated tetraploid cotton. In addition, the current results illustrated that stem trichome can be used as a morphological index of fiber quality in cotton conventional breeding.

Background: Upland cotton (Gossypium hirsutum) accounts for more than 90% of annual world cotton output due to its high yield potential. However, yield traits and fiber quality traits exhibit negative correlations in most cases. Here, to dissect simultaneously the genetic basis underlying complex traits such as yield and fiber quality as well as their genetic correlations in upland cotton, four F2 populations were constructed using two normal lines and two introgression lines. Subsequently, phenotyping of 8 agronomic and economic traits along with QTL mapping were implemented.Results: Extensive phenotype variations and transgressive segregation were found across segregation populations. Four genetic maps with length of 585.97cM, 752.45cM, 752.45cM and 1163.66cM were construct. The result of mapping displayed a total of 50 QTLs across four populations were identified, of which 27 were for fiber quality traits and 16 for yield traits. Multiple QTLs having the common maker, such as qBW4 and qBW2, or residing in the same QTL cluster, such as qLP9 and qFL9-1, were prioritized for further research.Conclusions: These findings will provide insight into simultaneous improvement of yield and fiber quality in upland cotton breeding.