Manufacturing Division, Yamasa Corporation, Choshi, Chiba, Japan
Akita Research Institute of Food and Brewing (ARIF), Arayamachi, Akita, Japan.
Appl Environ Microbiol. 2017 Dec 15;84(1). doi: 10.1128/AEM.01845-17. Print 2018 Jan 1.
In soy sauce manufacturing, plays a role in the production of volatile flavor compounds, such as volatile phenols, but limited accessible information on its genome has prevented further investigation regarding aroma production and breeding. Although the draft genome sequence data of two strains of have recently been reported, these strains are not similar to each other. Here, we reassess the draft genome sequence data for strain t-1, which was originally reported to be , and conclude that strain t-1 is most probably not but a gamete of hybrid Phylogenetic analysis of the D1/D2 region of the 26S ribosomal DNA (rDNA) sequence indicated that strain t-1 is more similar to the genus than to Moreover, we found that the genome of strain t-1 is composed of haploid genome content and divided into two regions that show approximately 100% identity with the T or P subgenome derived from the natural hybrid , such as NBRC110957 and NBRC1876. We also found a chromosome crossing-over signature in the scaffolds of strain t-1. These results suggest that strain t-1 is a gamete of the hybrid , generated by either meiosis or chromosome loss following reciprocal translocation between the T and P subgenomes. Although it is unclear why strain t-1 was misidentified as , the genome of strain t-1 has broad implications for considering the evolutionary fate of an allodiploid. In yeast, crossing between different species sometimes leads to interspecies hybrids. The hybrid generally cannot produce viable spores because dissimilarity of parental genomes prevents normal chromosome segregation during meiotic division, leading to a dead end. Thus, only a few natural cases of homoploid hybrid speciation, which requires mating between 1n gametes of hybrids, have been described. However, a recent study provided strong evidence that homoploid hybrid speciation is initiated in natural populations of the budding yeast, suggesting the potential presence of viable 1n gametes of hybrids. The significance of our study is finding that the strain t-1, which had been misidentified as , is a viable 1n gamete derived from hybrid .
在酱油酿造过程中，米曲霉在挥发性风味化合物的产生中发挥作用，例如挥发性酚类物质，但由于对其基因组的了解有限，因此无法进一步研究其香气的产生和育种。尽管最近报道了两个米曲霉菌株的基因组草图序列数据，但这些菌株彼此之间并不相似。在这里，我们重新评估了最初被报道为米曲霉的菌株 t-1 的基因组草图序列数据，并得出结论，菌株 t-1 很可能不是米曲霉，而是杂种米曲霉的配子。基于 26S 核糖体 DNA（rDNA）D1/D2 区序列的系统发育分析表明，菌株 t-1 与节旋菌属的亲缘关系比米曲霉更近。此外，我们发现菌株 t-1 的基因组由单倍体基因组组成，并分为两个区域，这两个区域与来自自然杂种如 NBRC110957 和 NBRC1876 的 T 或 P 亚基因组具有约 100%的同一性。我们还在菌株 t-1 的支架中发现了染色体交叉的特征。这些结果表明，菌株 t-1 是杂种米曲霉的配子，是由 T 和 P 亚基因组之间的减数分裂或染色体丢失形成的。尽管尚不清楚为什么菌株 t-1 被错误地鉴定为米曲霉，但菌株 t-1 的基因组对于考虑异源二倍体的进化命运具有广泛的意义。在酵母中，不同物种之间的杂交有时会导致种间杂种。由于亲本基因组的不相似性，在减数分裂过程中阻止了正常的染色体分离，杂种通常无法产生有活力的孢子，从而导致死胡同。因此，只有少数同源多倍体杂种形成的自然案例被描述，这需要杂种的 1n 配子之间的交配。然而，最近的一项研究提供了强有力的证据，表明同源多倍体杂种形成是在酿酒酵母的自然种群中启动的，这表明存在有活力的杂种 1n 配子的可能性。我们研究的意义在于发现曾经被错误鉴定为米曲霉的菌株 t-1 是源自杂种米曲霉的有活力的 1n 配子。
