Sharon A, Yamaguchi K, Christiansen S, Horwitz B A, Yoder O C, Turgeon B G
Botany Department, Tel-Aviv University, Israel.
Mol Gen Genet. 1996 Apr 24;251(1):60-8. doi: 10.1007/BF02174345.
The availability of cloned genes that control sexual reproduction (mating type genes) in high fungi has allowed us to consider the causes of failure to mate in asexual fungi. We report here that the asexual fungus Bipolaris sacchari has a homolog of the MAT-2 gene of its sexual ascomycete relative Cochliobolus heterostrophus. The B. sacchari MAT-2 sequence is highly similar to that of C. heterostrophus MAT-2 and, in fact, functions in transgenic C. heterostrophus. Thus, the asexual nature of B. sacchari is not due to absence or mutation of MAT. When either of the C. heterostrophus MAT genes was transformed into B. sacchari, the recipient could neither self nor cross with other B. sacchari strains, in contrast to transgenic C. heterostrophus strains which can do both. Persistent asexuality of B. sacchari, in spite of the presence of complementary functional MAT genes, suggests that this fungus lacks genes other than MAT which are essential for mating. Notably, the transgenic B. sacchari strains were sometimes able to initiate, but not complete, sexual development in interspecific pairings with C. heterostrophus. Transcript analysis showed that the B. sacchari MAT-2 gene is expressed in transgenic C. heterostrophus and that the C. heterostrophus MAT genes are expressed in transgenic B. sacchari. No transcript of the native B. sacchari MAT-2 gene was detected under any growth condition tested.
控制高等真菌有性生殖的克隆基因（交配型基因）的可得性，使我们能够思考无性真菌无法交配的原因。我们在此报告，无性真菌甘蔗平脐蠕孢（Bipolaris sacchari）有其有性子囊菌亲缘种玉米小斑病菌（Cochliobolus heterostrophus）的MAT-2基因的同源物。甘蔗平脐蠕孢MAT-2序列与玉米小斑病菌MAT-2序列高度相似，实际上，它在转基因玉米小斑病菌中发挥功能。因此，甘蔗平脐蠕孢的无性本质并非由于MAT的缺失或突变。当将玉米小斑病菌的任一MAT基因转化到甘蔗平脐蠕孢中时，受体既不能自体交配，也不能与其他甘蔗平脐蠕孢菌株杂交，这与能够进行这两种交配的转基因玉米小斑病菌菌株形成对比。尽管存在互补的功能性MAT基因，甘蔗平脐蠕孢仍持续无性，这表明该真菌缺乏除MAT之外对交配至关重要的基因。值得注意的是，转基因甘蔗平脐蠕孢菌株在与玉米小斑病菌的种间配对中有时能够启动但不能完成有性发育。转录分析表明，甘蔗平脐蠕孢MAT-2基因在转基因玉米小斑病菌中表达，而玉米小斑病菌MAT基因在转基因甘蔗平脐蠕孢中表达。在任何测试的生长条件下均未检测到天然甘蔗平脐蠕孢MAT-2基因的转录本。
