An APSES Transcription Factor Xbp1 Is Required for Sclerotial Development, Appressoria Formation, and Pathogenicity in Ciboria shiraiana.

Shuai Zhang,Boning Cao,Panpan Zhu,Ruolan Li,Shuyu Ma,Aichun Zhao,Xie Wang

doi:10.3389/fmicb.2021.739686

Abstract

Sclerotinia diseases are important plant fungal diseases that, causes huge economic worldwide losses every year. Ciboria shiraiana is the main pathogen that results in mulberry sclerotia diseases. Sclerotia and appressoria play important roles in long-term pathogen survival and in host infection during life and disease cycles. However, the molecular mechanisms of sclerotial development and appressoria formation in C. shiraiana have not been well studied. Here, an Asm1p, Phd1p, Sok2p, Efg1p and StuAp (APSES)-type transcription factor in C. shiraiana, CsXbp1, involved in sclerotial development and appressoria formation was functionally characterized. Bioinformatics analyses showed that CsXbp1 contained an APSES-type DNA binding domain. The expression levels of CsXbp1 were higher in sclerotia and during later stages of infection. Compared with wild-type strains, hyphal growth was slower, the number and weight of sclerotia were reduced significantly, and appressoria formation was obviously delayed in CsXbp1 RNA interference (RNAi) strains. Moreover, the CsXbp1 RNAi strains showed weakened pathogenicity owing to compound appressoria defects. Tobacco rattle virus-mediated host-induced gene silencing enabled Nicotiana benthamiana to increase its resistance to C. shiraiana by reducing the CsXbp1 transcripts level. Thus, CsXbp1 plays vital roles in sclerotial formation, appressoria formation, and pathogenicity in C. shiraiana. This study provides new insights into the infection mechanisms of C. shiraiana and plant resistance breeding.

Highlights

Ciboria shiraiana, in the filamentous fungal genus Ciboria, family Sclerotiniaceae, order Helotiales of the Ascomycota (Whetzel and Wolf, 1945), is the major fungal pathogen of mulberry sclerotinia diseases, which lead to substantial reductions in production and consequent economic losses (Gray and Richard, 1987; Lv et al, 2011)
A putative fungal-specific transcription factor protein was identified in the genome of C. shiraiana and named CsXbp1(Cs01344) because of its homology to Botrytis cinerea BcXbp1
A structural analysis of CsXbp1 revealed that it contained a fungal-specific APSES-type DNA binding domain (IPR003163) that, was located from 110 to 228 aa (Figure 1A)

Summary

Introduction

In the filamentous fungal genus Ciboria, family Sclerotiniaceae, order Helotiales of the Ascomycota (Whetzel and Wolf, 1945), is the major fungal pathogen of mulberry sclerotinia diseases, which lead to substantial reductions in production and consequent economic losses (Gray and Richard, 1987; Lv et al, 2011). CsXbp Is Involved in Pathogenicity temperature, the sclerotia break dormancy to generate ascospores that are released and infect the female flowers of mulberry trees. Hyphae entangle to form sclerotia in the infected mulberry fruit. The diseased fruit falls into the soil, and the sclerotia stay dormant in the soil until conditions are suitable for the infection cycle (Lv et al, 2019). The compound appressorium is a multicellular infection structure that differentiates from the top of a hypha formed by pathogen. It attaches to the host surface and penetrates the plant cuticle, which helps the pathogen colonize the host plant (Uloth et al, 2016). It is necessary to study the growth and development of sclerotia and appressoria

Methods

Results

Conclusion