Abstract：
In this study, the whole HD-Zip family members of G. hirsutum were identified, and GhHDZ76 was classified into the HD-Zip IV subgroup. GhHDZ76 was predominantly expressed in the 0-5 DPA of fiber development stage and localized in the nucleus. Overexpression of GhHDZ76 significantly increased the length and density of trichomes in Arabidopsis thaliana. The fiber length of GhHDZ76 knockout lines by CRISPR/Cas9 was significantly shorter than WT at the early elongation and mature stage, indicating that GhHDZ76 positively regulate the fiber elongation. Scanning electron microscopy showed that the number of ovule surface protrusion of 0 DPA of GhHDZ76 knockout lines was significantly lower than WT, suggesting that GhHDZ76 can also promote the initiation of fiber development. The transcript level of GhWRKY16, GhRDL1, GhEXPA1 and GhMYB25 genes related to fiber initiation and elongation in GhHDZ76 knockout lines were significantly decreased. Yeast two-hybrid and Luciferase complementation imaging (LCI) assays showed that GhHDZ76 can interact with GhWRKY16 directly. As a transcription factor, GhHDZ76 has transcriptional activation activity, which could bind to L1-box elements of the promoters of GhRDL1 and GhEXPA1. Double luciferase reporter assay showed that the GhWRKY16 could enhance the transcriptional activity of GhHDZ76 to pGhRDL1, but it did not promote the transcriptional activity of GhHDZ76 to pGhEXPA1. GhHDZ76 protein may also promote the transcriptional activity of GhWRKY16 to the downstream target gene GhMYB25. Our results provided a new gene resource for fiber development and a theoretical basis for the genetic improvement of cotton fiber quality.
摘要：
在这项研究中,整个HD-Zip家族成员的G.hirsutum被确认，GhHDZ76分为HD-ZipIV亚组。GhHDZ76主要在纤维发育阶段的0-5DPA中表达，并位于细胞核中。GhHDZ76的过表达显着增加了拟南芥毛状体的长度和密度。通过CRISPR/Cas9敲除GhHDZ76的纤维长度在早期伸长和成熟期明显短于WT，表明GhHDZ76正向调节纤维伸长率。扫描电子显微镜显示，GhHDZ76敲除系的0DPA胚珠表面突起数显著低于WT，表明GhHDZ76还可以促进纤维发育的启动。GhHDZ76敲除品系中与纤维起始和伸长相关的GhWRKY16、GhRDL1、GhEXPA1和GhMYB25基因的转录水平显著降低。酵母双杂交和荧光素酶互补成像（LCI）分析表明，GhHDZ76可以直接与GhWRKY16相互作用。作为转录因子,GhHDZ76具有转录激活活性，它可以与GhRDL1和GhEXPA1启动子的L1盒元件结合。双荧光素酶报告基因实验表明，GhWRKY16可以增强GhHDZ76对pGhRDL1的转录活性，但不能促进GhHDZ76对pGhEXPA1的转录活性。GhHDZ76蛋白还可能促进GhWRKY16对下游靶基因GhMYB25的转录活性。研究结果为棉纤维发育提供了新的基因资源,为棉纤维品质的遗传改良提供了理论依据。
