《自然》：科学家发现孟德尔分离定律发生机制

2010/08/21 05:35:24

这一发现将有助于对植物品种进行改良

日本奈良尖端科学技术大学院大学的研究人员在8月19日的英国《自然》杂志上报告说，他们发现了动植物遗传过程中，显性基因得以表达，而隐性基因表达被抑制的原因。这一发现将有助于对植物品种进行改良。

很多动植物都会将体内的部分基因遗传给下一代，但是子一代在很多情况下只表达出基于一方基因的性状（显性性状），而基于另一方基因的性状（隐性性状）则被暂时隐藏而未表现；在子二代中，上述显性基因和隐性基因都有所表达。这样的遗传规律被称为“孟德尔分离定律”。

奈良尖端科学技术大学院大学教授高山诚司和研究员樽谷芳明率领的小组以一种日本土生油菜为对象进行研究。他们发现，位于显性基因附近的某种基因指导合成了一种低分子核糖核酸，导致隐性基因甲基化，其作用从而被遏制。研究小组推测动物也可能存在类似机制。

高山诚司2006年曾发现隐性基因由于化学反应而无法发挥作用，此次发现则弄清了隐性基因受到遏制的具体机制。

 

高山诚司指出，植物显性遗传的性状通常是优势性状。以此次发现为基础，有可能通过人工手段，只利用优势性状对植物的品种进行改良。

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Trans-acting small RNA determines dominance relationships in Brassica self-incompatibility

Yoshiaki Tarutani,Hiroshi Shiba, Megumi Iwano, Tomohiro Kakizaki,Go Suzuki, Masao Watanabe, Akira Isogai & Seiji Takayama

Nature 2010, 466: 983–986. DOI: doi:10.1038/nature09308

A diploid organism has two copies of each gene, one inherited from each parent. The expression of two inherited alleles is sometimes biased by the effects known as dominant/recessive relationships, which determine the final phenotype of the organism. To explore the mechanisms underlying these relationships, we have examined the monoallelic expression of S-locus protein 11 genes (SP11), which encode the male determinants of self-incompatibility in Brassica. We previously reported that SP11 expression was monoallelic in some S heterozygotes, and that the promoter regions of recessive SP11 alleles were specifically methylated in the anther tapetum. Here we show that this methylation is controlled by trans-acting small non-coding RNA (sRNA). We identified inverted genomic sequences that were similar to the recessive SP11 promoters in the flanking regions of dominant SP11 alleles. These sequences were specifically expressed in the anther tapetum and processed into 24-nucleotide sRNA, named SP11 methylation inducer (Smi). Introduction of the Smi genomic region into the recessive S homozygotes triggered the methylation of the promoter of recessive SP11 alleles and repressed their transcription. This is an example showing sRNA encoded in the flanking region of a dominant allele acts in trans to induce transcriptional silencing of the recessive allele. Our finding may provide new insights into the widespread monoallelic gene expression systems.