The false smut pathogen Ustilaginoidea virens requires rice stamens for false smut ball formation.

Jing Fan,Yan Li,Ping Li,Li Wang,Guo‐Bang Li,Jie Liu,Juan Yang,Min He,Xiaoyun Wu ,Dongwei Hu ,Ya-Lin Huang ,Yufeng Zhou ,Jinlong Wu ,Xiao-Qiong Chen ,Yuqiu Wang ,Zhao Jun ,Zhiyou Gong ,Xiao-Hong Hu ,Shuangcheng Li ,Peizhou Xu ,Wenming Wang

doi:10.1111/1462-2920.14881

Abstract

SummaryRice false smut has emerged as a serious grain disease in rice production worldwide. The disease is characterized by the transformation of individual rice florets into false smut balls, which is caused by the fungal pathogen Ustilaginoidea virens. To date, little is known about the host factors required for false smut ball formation by U. virens. In this study, we identified histological determinants for the formation of false smut balls by inoculating U. virens into rice floral mutants defective with respect to individual floral parts. The results showed that U. virens could form mature false smut balls in rice floral mutants with defective pistils, but failed to develop false smut balls in the superwoman mutant lacking stamens, identifying that U. virens requires rice stamens to complete its infection cycle. Comparative transcriptome analysis indicated a list of candidate host genes that may facilitate nutrient acquisition by U. virens from the rice stamens, such as SWEET11, SWEET14 and SUT5, and genes involved in the biosynthesis of trehalose and raffinose family sugars. These data pinpoint rice stamens as the key target organ of U. virens infection and provide a valuable starting point for dissecting the molecular mechanism of false smut ball formation.

Highlights

Rice false smut disease is caused by the ascomycete fungal phytopathogen Ustilaginoidea virens (Cooke) Takahashi (Fan et al, 2016a)
False smut balls are covered with chlamydospores that become orange or green (Wang et al, 2019) and generate sclerotia when exposed to large day/night temperature differences (Fan et al, 2016b)
As chlamydospores and sclerotia are produced from false smut balls and are the primary inocula of the rice false smut disease (Ikegami, 1960; Fan et al, 2010; Yong et al, 2018), understanding the factors involved in the formation of false smut ball is significant for controlling the disease

Summary

Introduction

Rice false smut disease is caused by the ascomycete fungal phytopathogen Ustilaginoidea virens (Cooke) Takahashi (teleomorph: Villosiclava virens) (Fan et al, 2016a). This disease has been reported with increasing occurrence in most rice production areas worldwide (Brooks et al, 2009; Ladhalakshmi et al, 2012; Jecmen and TeBeest, 2015). U. virens interrupts the process of rice flowering and fertilization and hijacks host nutrients for mycelial growth and false smut ball formation (Fan et al, 2015; Song et al, 2016). The intercellular infection of U. virens in the ovary was further confirmed by TEM analysis (Fig. 5O)

Results

Discussion

Conclusion