稻曲菌交配型初探

 稻曲菌（有性态：Villosiclava virens；无性态：Ustilaginoidea virens）有性繁殖产生的子囊孢子是水稻稻曲病可能的初侵染源之一，交配型基因座对真菌有性繁殖中的性别控制起着决定性作用。为进一步揭示稻曲菌的有性繁殖方式，本研究首次克隆了稻曲菌交配型基因mat1-1-1的α-结构域（α-domain）相应核苷酸序列，发现其与麦角菌科真菌Cordyceps militaris、Cor. bassiana和Claviceps purpurea的mat1-1-1基因中α-结构域相应核苷酸序列同源性分别为61%、63%和68%；根据mat1-1-1和mat1-2-1部分基因序列设计特异性引物，并使用PCR方法检测了来源于3个异源子座的240个子囊孢子单孢菌株和50个田间菌株的交配型基因，结果显示稻曲菌mat1-1-1和mat1-2-1基因分别存在于不同菌株中；将具有相同或不同交配型基因的菌株配对接种，发现菌核通常产生在mat1-1-1和mat1-2-1基因型菌株配对接种产生的稻曲球上，其中大部分菌核可萌发产生子座，而菌株单独接种或具有相同交配型基因的菌株配对接种水稻后多数不能形成菌核；根据以上结果初步推断稻曲菌为异宗配合真菌。

Preliminary study on mating system of Villosiclava virens

Villosiclava virens, the causal agent of rice false smut, produces ascospores in sexual propagation, which could be one of the primary infection sources of the disease. To better understand its sexual life cycle, the mating-type genes of V. viren were initially studied to reveal its sexual propagation in this paper. The 185 base-pair (bp) conserved coding sequence of housekeeping α-domain of mat1-1-1 mating-type protein was cloned, and this sequence had a similarity of 61%, 63% and 68% to that of Cordyceps militaris, Cor. bassiana and Claviceps purpurea, respectively. Two pairs of specific primers were designed according to the partial sequences of mat1-1-1 and mat1-2-1 mating-type genes in V. viren strains, the 138 bp and 220 bp length DNA fragments could be amplified by PCR respectively. Two hundred and forty single-ascospore strains isolated from three stromata on different sclerotium and 50 randomly selected field isolates of V. viren were employed in the test. And it was found that mat1-1-1 and mat1-2-1 mating-type genes existed in the alternative type of strains. The subsequent inoculation assay further proved that V. viren was a heterothallic fungus, since almost all the sclerotia and fertile perithecia were observed upon pair-inoculated strains of “mat1-1-1” and “mat1-2-1” type, and barely observed upon inoculated strains of “mat1-1-1” or “mat1-2-1” type.