Mating system of Ustilago esculenta and its polymorphism

Abstract

Zizania latifolia Turcz., which is mainly distributed in Asia, has had a long cultivation history as a cereal and vegetable crop. On infection with the smut fungus Ustilago esculenta, Z. latifolia becomes an edible vegetable, water bamboo. Two main cultivars, with a green shell and red shell, are cultivated for commercial production in Taiwan. Previous studies indicated that cultivars of Z. latifolia may be related to infection with U. esculenta isolates. However, related research is limited. The infection process of the corn smut fungus Ustilago maydis is coupled with sexual development and under control of the mating type locus. Thus, we aimed to use knowledge of U. maydis to reveal the mating system of U. esculenta. We collected water bamboo and isolated 145 U. esculenta strains from Taiwans major production areas. By using PCR and idiomorph screening among meiotic offspring and field isolates, we identified three idiomorphs of the mating type locus and found no sequence recombination between them. Whole-genome sequencing (Illumina and Pacbio) suggested that the mating system of U. esculenta was bipolar. Mating type locus 1 (MAT-1) was 555,862 bp, and contained 44% repeated sequences. Sequence comparison revealed that U. esculenta MAT-1 shared better conservation with the sex chromosome of U. maydis than U. hordei. These results can be utilized to further explore the genomic diversity of U. esculenta isolates and their application for water bamboo breeding.