Identification and Functional Analysis of the Pheromone Response Factor Gene of Sporisorium scitamineum.

Guining Zhu,Enping Cai,Guobing Cui,Chengwu Zou,Yizhen Deng,Changqing Chang,Bin Zhang,Zide Jiang,Zhiqiang Wang,Baoshan Chen,Meixin Yan,Pinggen Xi

doi:10.3389/fmicb.2019.02115

Abstract

The sugarcane smut fungus Sporisorium scitamineum is bipolar and produces sporidia of two different mating types. During infection, haploid cells of opposite mating types can fuse to form dikaryotic hyphae that can colonize plant tissue. Mating and filamentation are therefore essential for S. scitamineum pathogenesis. In this study, we obtained one T-DNA insertion mutant disrupted in the gene encoding the pheromone response factor (Prf1), hereinafter named SsPRF1, of S. scitamineum, via Agrobacterium tumefaciens-mediated transformation (ATMT) mutagenesis. Targeted deletion of SsPRF1 resulted in mutants with phenotypes similar to the T-DNA insertion mutant, including failure to mate with a compatible wild-type partner strain and being non-pathogenic on its host sugarcane. qRT-PCR analyses showed that SsPRF1 was essential for the transcription of pheromone-responsive mating type genes of the a1 locus. These results show that SsPRF1 is involved in mating and pathogenicity and plays a key role in pheromone signaling and filamentous growth in S. scitamineum.

Highlights

Sugarcane smut caused by Sporisorium scitamineum is a devastating disease in sugarcane worldwide
Sporisorium reilianum, a smut fungus closely related to U. maydis, possesses three a alleles containing two active pheromone genes each, and at least five alleles for the b locus, that govern its ability of sexual mating and dimorphic switching essential for virulence (Schirawski et al, 2005)
S. scitamineum is a dimorphic pathogen with two different life styles, a saprophytic stage growing by budding as unicellular sporidia, and a pathogenic stage growing as dikaryotic hyphae

Summary

Introduction

Sugarcane smut caused by Sporisorium scitamineum is a devastating disease in sugarcane worldwide. The most recognizable characteristic of this disease is a black or gray growth from the top of plant cane that is referred to as a “smut whip” that is composed of a central core of pithy plant tissue surrounded by the fruiting structures of the fungus and the brown to black teliospores (Croft and Braithwaite, 2006; Sundar et al, 2012). Sporidia of different mating types can fuse to form pathogenic dikaryotic hyphae to infect sugarcane buds and the hyphae grow within the meristematic tissue, eventually producing whip-like fruiting structure and teliospores in the infected plants. The diploid teliospores germinate and undergo meiosis to yield haploid sporidia, which need to mate again to infect the plant and to initiate a round of infection (Albert and Schenck, 1996; Croft and Braithwaite, 2006; Yan et al, 2016b). Mating plays a central role in the life cycle of smut pathogens, as it initiates parasitism by a morphological and Sugarcane Smut Fungus PRF1 physiological transition from saprotrophic yeast cells to pathogenic filaments (Hartmann et al, 1996; Bakkeren et al, 2008; Kellner et al, 2011)

Methods

Results

Conclusion