GhMAP3K65, a Cotton Raf-Like MAP3K Gene, Enhances Susceptibility to Pathogen Infection and Heat Stress by Negatively Modulating Growth and Development in Transgenic Nicotiana benthamiana

Abstract

Mitogen-activated protein kinase kinase kinases (MAP3Ks), the top components of MAPK cascades, modulate many biological processes, such as growth, development and various environmental stresses. Nevertheless, the roles of MAP3Ks remain poorly understood in cotton. In this study, <i>GhMAP3K65</i> was identified in cotton, and its transcription was inducible by pathogen infection, heat stress, and multiple signalling molecules. Silencing of <i>GhMAP3K65</i> enhanced resistance to pathogen infection and heat stress in cotton. In contrast, overexpression of <i>GhMAP3K65</i> enhanced susceptibility to pathogen infection and heat stress in transgenic <i>Nicotiana benthamiana</i>. The expression of defence-associated genes was activated in transgenic <i>N. benthamiana</i> plants after pathogen infection and heat stress, indicating that <i>GhMAP3K65</i> positively regulates plant defence responses. Nevertheless, transgenic <i>N. benthamiana</i> plants impaired lignin biosynthesis and stomatal immunity in their leaves and repressed vitality of their root systems. In addition, the expression of lignin biosynthesis genes and lignin content were inhibited after pathogen infection and heat stress. Collectively, these results demonstrate that <i>GhMAP3K65</i> enhances susceptibility to pathogen infection and heat stress by negatively modulating growth and development in transgenic <i>N. benthamiana</i> plants.