Abstract
BackgroundUstilago esculenta, a pathogenic basidiomycete fungus, infects Zizania latifolia to form edible galls named Jiaobai in China. The distinct growth conditions of U. esculenta induced Z. latifolia to form three different phenotypes, named male Jiaobai, grey Jiaobai and white Jiaobai. The aim of this study is to characterize the genetic and morphological differences that distinguish the two U. esculenta strains.ResultsIn this study, sexually compatible haploid sporidia UeT14/UeT55 from grey Jiaobai (T strains) and UeMT10/UeMT46 from white Jiaobai (MT strains) were isolated. Meanwhile, we successfully established mating and inoculation assays. Great differences were observed between the T and MT strains. First, the MT strains had a defect in development, including lower teliospore formation frequency and germination rate, a slower growth rate and a lower growth mass. Second, they differed in the assimilation of nitrogen sources in that the T strains preferred urea and the MT strains preferred arginine. In addition, the MT strains were more sensitive to external signals, including pH and oxidative stress. Third, the MT strains showed an infection defect, resulting in an endophytic life in the host. This was in accordance with multiple mutated pathogenic genes discovered in the MT strains by the non-synonymous mutation analysis of the genome re-sequencing data between the MT and T strains (GenBank accession numbers of the genome re-sequencing data: JTLW00000000 for MT strains and SRR5889164 for T strains).ConclusionThe MT strains appeared to have defects in growth and infection and were more sensitive to external signals compared to the T strains. They displayed an absolutely stable endophytic life in the host without an infection cycle. Accordingly, they had multiple gene mutations occurring, especially in pathogenicity. In contrast, the T strains, as phytopathogens, had a complete survival life cycle, in which the formation of teliospores is important for adaption and infection, leading to the appearance of the grey phenotype. Further studies elucidating the molecular differences between the U. esculenta strains causing differential host phenotypes will help to improve the production and formation of edible white galls.
Highlights
Ustilago esculenta, a pathogenic basidiomycete fungus, infects Zizania latifolia to form edible galls named Jiaobai in China
The haploid sporidia of U. esculenta were isolated from the teliospores of the swollen tissues of white Jiaobai and grey Jiaobai of the Longjiao 2# cultivar, and sexually compatible sporidia were isolated
This may be related to the separated a3 locus that existed in the UeMT10 strain (Additional file 3) or strain variability, The defect in the infection of MT strains led to an incomplete life cycle and an absolute endophytic life In the present study, a similar incomplete life cycle for the T and MT strains in vitro was drawn
Summary
A pathogenic basidiomycete fungus, infects Zizania latifolia to form edible galls named Jiaobai in China. In China, some plants appeared in the fields with galls full of dark-coloured teliospores (Additional file 1b), named “grey Jiaobai”. Those grey Jiaobai should be discarded immediately in fields to ensure yields because only “white Jiaobai” have economic value in China and are counted in the yield. It is hypothesized that through continuous artificial selection, white Jiaobai may have developed a special plant-fungus interaction, resulting in edible galls with better nutritional and medicinal value. If farmers do not remove grey Jiaobai immediately, the incidence rate of grey Jiaobai and male Jiaobai increases in the rounds of harvest
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