Kronstad J W, Leong S A
Department of Microbiology, University of British Columbia, Vancouver, Canada.
Genes Dev. 1990 Aug;4(8):1384-95. doi: 10.1101/gad.4.8.1384.
The b locus of the phytopathogenic fungus Ustilago maydis encodes a multiallelic recognition function that controls the ability of the fungus to form a dikaryon and complete the sexual stage of the life cycle. The b locus has at least 25 alleles and any combination of two different alleles, brought together by mating between haploid cells, allows the fungus to cause disease and undergo sexual development within the plant. An open reading frame of 410 amino acids has been shown to specify a polypeptide responsible for the activity of the b1 allele, and comparisons of the predicted amino acid sequences for 6 b alleles allowed identification of variable and constant regions within the coding region of the gene. Haploid strains carrying a null mutation at the b locus, created by gene disruption, are viable but fail to interact with formerly compatible strains to give an infectious dikaryon. Analysis of mutants carrying a null allele indicated that the products of different alleles of the b locus combine to form a new regulatory activity and that this activity directly or indirectly turns on the pathway leading to sexual development and pathogenesis.
植物致病真菌玉米黑粉菌的b位点编码一种多等位基因识别功能，该功能控制着真菌形成双核体并完成生命周期有性阶段的能力。b位点至少有25个等位基因，通过单倍体细胞之间的交配聚集在一起的任意两个不同等位基因的组合，都能使真菌在植物体内致病并进行有性发育。一个由410个氨基酸组成的开放阅读框已被证明可指定一种负责b1等位基因活性的多肽，对6个b等位基因的预测氨基酸序列进行比较，能够确定该基因编码区内的可变区和恒定区。通过基因破坏在b位点产生无效突变的单倍体菌株是可行的，但无法与先前相容的菌株相互作用以产生感染性双核体。对携带无效等位基因的突变体进行分析表明，b位点不同等位基因的产物结合形成一种新的调节活性，并且这种活性直接或间接地开启导致有性发育和致病的途径。
