Laity C, Giasson L, Campbell R, Kronstad J
Biotechnology Laboratory, University of British Columbia, Vancouver, Canada.
Curr Genet. 1995 Apr;27(5):451-9. doi: 10.1007/BF00311215.
Mating and pathogenesis of the corn smut fungus, Ustilago maydis, are controlled by two unlinked mating-type loci, a and b. Yeast-like haploids that differ at both loci are compatible and fuse to establish a pathogenic dikaryon. Mating is assayed in vitro by co-inoculation on culture medium containing activated charcoal; compatible combinations have a characteristic "fuzzy" appearance caused by the growth of aerial hyphae. In general, this test has not been useful for assaying the mating ability of strains that are already mycelial (e.g., those heterozygous at b or at both mating-type loci). Using an assay for cytoduction involving transfer of a mitochondrial marker during transient cell fusion, and engineered strains with defined genotypes, we examined the mating abilities of strains heterozygous or hemizygous at the mating-type loci. The data (which have not been available from conventional pathogenicity or plate mating tests) show that heterozygosity at b attenuates fusion in haploid and diploid strains, whereas strains heterozygous at a retain the ability to fuse with a compatible haploid partner. It appears, therefore, that subsequent fusion events are attenuated once fusion has occurred to establish the U. maydis dikaryon.
玉米瘤黑粉菌（Ustilago maydis）的交配和致病过程由两个不连锁的交配型基因座a和b控制。在这两个基因座上存在差异的酵母样单倍体是可亲和的，并融合形成致病双核体。交配能力通过在含有活性炭的培养基上共同接种来进行体外检测；亲和组合会因气生菌丝的生长而呈现出特征性的“绒毛状”外观。一般来说，该检测方法对于检测已经是菌丝体的菌株（例如在b基因座或两个交配型基因座上杂合的菌株）的交配能力并无帮助。我们利用一种涉及在瞬时细胞融合过程中线粒体标记转移的细胞减数分裂检测方法，并使用具有特定基因型的工程菌株，研究了在交配型基因座上杂合或半合子的菌株的交配能力。这些数据（传统的致病性或平板交配检测无法获得）表明，b基因座杂合会减弱单倍体和二倍体菌株的融合，而a基因座杂合的菌株仍保留与可亲和单倍体伙伴融合的能力。因此，一旦融合发生以建立玉米瘤黑粉菌双核体，后续的融合事件似乎就会减弱。
