Genome-Wide Identification of the HD-ZIP III Subfamily in Upland Cotton Reveals the Involvement of GhHB8-5D in the Biosynthesis of Secondary Wall in Fiber and Drought Resistance.

Shuaijie Li,Yuke Cui,Wenliang Xu,Ye Wang,Le Liu,Jie Zhang,Mengru Feng,Fuguang Li,Yanan Gao

doi:10.3389/fpls.2021.806195

Abstract

A subfamily of transcription factors known as HD-ZIP III plays distinct roles in the secondary cell wall biosynthesis, which could be attributed to the quality of cotton fiber and adaptation to drought stress. In this study, 18 HD-ZIP III genes were identified as genome wide from the upland cotton (Gossypium hirsutum). These genes are distributed on 14 different chromosomes, and all of them have undergone segmental duplications. Numerous cis-elements were identified in the promoter regions, which are related to phytohormone responses and abiotic stresses. Expression profiling of these genes by quantitative real-time (qRT)-PCR illustrated their differential spatial expression, with preferential expression in cotton fiber. Among these genes, GhHB8-5D was predicted to encode a protein that is targeted to the cell nucleus and having self-activation ability. In addition, the ectopic expression of GhHB8-5D or its synonymous mutant GhHB8-5Dm in Arabidopsis resulted in stunted plant growth, curly leaves, and twisted inflorescence stems. Microscopy examination revealed that the morphology of vascular bundles and deposition of secondary wall had substantially altered in stems, which is concomitant with the significant alteration in the transcription levels of secondary wall-related genes in these transgenic Arabidopsis. Further, ectopic expression of GhHB8-5D or GhHB8-5Dm in Arabidopsis also led to significant increase in green seedling rate and reduction in root length relative to wild type when the plants were grown under mimicked drought stress conditions. Taken together, our results may shed new light on the functional roles of GhHB8-5D that is attributable for secondary cell wall thickening in response to drought stress. Such a finding may facilitate a novel strategy for improving plant adaptations to environmental changes via regulating the biosynthesis of secondary cell wall.

Highlights

As the most important crop producing natural fibers, upland cotton (Gossypium hirsutum) is broadly cultivated in the temperate regions in the world and the quality of fiber is of paramount economic significance (Paterson et al, 2012)
Transcriptional regulation network controlling secondary cell wall (SCW) biosynthesis has been extensively elucidated in the model plant Arabidopsis (Arabidopsis thaliana), in which numerous transcription factors (TFs) such as NAC acting as master switch coordinate the expression of cellulose synthase (CESA) by coupling with MYB and others (Taylor-Teeples et al, 2015; Zhong and Ye, 2015)
HD-ZIP III has been studied in several plants (Chai et al, 2018; Li et al, 2019; Sharif et al, 2020), this study represents the first comprehensive investigation on this subfamily of genes in cotton

Summary

Introduction

As the most important crop producing natural fibers, upland cotton (Gossypium hirsutum) is broadly cultivated in the temperate regions in the world and the quality of fiber is of paramount economic significance (Paterson et al, 2012). In cotton, only a limited number of TFs that regulate SCW synthesis have been identified, while their functionality and intricate relationship remain poorly understood (Zhang et al, 2018a; Huang et al, 2019, 2021; Cao et al, 2020). This is despite the recent premise of a model of a four-layered transcriptional regulatory network consisting of GhTCP4, GhMYB7, GhFSN1, and GhMYB46_D13 regulating fiber SCW GhCesA genes (Huang et al, 2021). Such a network model may still fall short in sophistication, as many other TFs that function in concert in SCW formation, such as HD-ZIP III TFs, remain unexplored (Robischon et al, 2011; Du et al, 2015)

Methods

Results

Conclusion