DELLA-NAC Interactions Mediate GA Signaling to Promote Secondary Cell Wall Formation in Cotton Stem.

Yi Wang,Yonglu Dai,Yuanyuan Qin,Jianyan Zeng,Xufen Ouyang,Zhong Chen,Lingfang Ran,Chuannan Wang,Yang Dou,Yiping Wu,Aimin Liang,Yuehua Xiao,Yaohua Li,Wanting Yu,Qingwei Suo

doi:10.3389/fpls.2021.655127

Abstract

Gibberellins (GAs) promote secondary cell wall (SCW) development in plants, but the underlying molecular mechanism is still to be elucidated. Here, we employed a new system, the first internode of cotton, and the virus-induced gene silencing method to address this problem. We found that knocking down major DELLA genes via VIGS phenocopied GA treatment and significantly enhanced SCW formation in the xylem and phloem of cotton stems. Cotton DELLA proteins were found to interact with a wide range of SCW-related NAC proteins, and virus-induced gene silencing of these NAC genes inhibited SCW development with downregulated biosynthesis and deposition of lignin. The findings indicated a framework for the GA regulation of SCW formation; that is, the interactions between DELLA and NAC proteins mediated GA signaling to regulate SCW formation in cotton stems.

Highlights

Plant secondary cell walls (SCWs) are important in adopting erect growth and land environment because they provide mechanical support and water transportation tunnels (Kumar et al, 2016)
The immunoblot analysis revealed that the DELLA protein level in the cotton stems was significantly lowered by GA and elevated upon PAC treatment (Figure 1D), indicating that the common GA signaling process, GA-induced DELLA degradation, functioned in the cotton stems
These results suggested that GA promoted stem elongation and SCW development via the mediation of the degradation of DELLA proteins in the cotton seedlings

Summary

Introduction

Plant secondary cell walls (SCWs) are important in adopting erect growth and land environment because they provide mechanical support and water transportation tunnels (Kumar et al, 2016). A conserved pyramid-shaped regulatory hierarchy has been identified to regulate gene expressions required for SCW formation in plants, especially in vascular tissues (Zhong et al, 2008; Nakano et al, 2015; Kumar et al, 2016; Zhao, 2016). This regulatory network contains basically three layers of transcription factors (TFs). In Arabidopsis, a group of NAC (NAM, ATAF1/2 and CUC2) family TFs, such as NAC secondary wall thickening (NST) promoting factors 1–3 and vascular-related NAC domains (VNDs) 1–7 (Zhong et al, 2006; Mitsuda et al, 2007; Yamaguchi et al, 2008; Zhou et al, 2014), comprise tier 3 and function as top master switches, which control the transcription of tier 2 TFs, such as MYB proteins (MYBs 46, 55, 61, 83, and 103) and NAC

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