Epigenetic inheritance in rice plants
Epigenetic inheritance in rice plants
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DOI：
10.1093/aob/mcm110
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发表时间：
2007-08-01
期刊：
影响因子：
4.2
通讯作者：
Sano, Hiroshi
中科院分区：
文献类型：
--
作者：
Akimoto, Keiko;Katakami, Hatsue;Sano, Hiroshi
背景与目的表观遗传学被定义为在不改变碱基序列的情况下调节基因表达的机制。一个分子基础被认为是DNA胞嘧啶甲基化，它可逆地改变DNA或染色质结构。尽管它与几代人的表观遗传的相关性已经间接地被证明，但在基因水平上的证据是有限的。本研究旨在寻找其甲基化状态与表型遗传直接相关的基因。方法通过处理水稻(Oryza Sativa SSP)来人工降低体内DNA甲基化。用5-氮杂脱氧胞苷(5-azadeoxcytidine，5-azadeoxcytidine)种子和后代在大田里栽培10年。用甲基化敏感的扩增多态(MSAP)方法筛选甲基化状态改变的基因组区域，用亚硫酸氢法直接扫描胞嘧啶甲基化。水稻白叶枯病菌的病原菌感染。用剪刀浸渍法对成熟叶片进行水稻PR2小种鉴定。结果多数幼苗致死，但也有部分存活至成熟。其中一个被命名为Line-2的品系表现出明显的矮秆标记表型，其后代在9个世代中稳定遗传。MSAP筛选得到6个片段，其中2个片段进一步用DNA印迹杂交和直接甲基化定位进行了鉴定。一个编码反转录转座子Gag-Poll多聚蛋白的克隆显示，Line-2中的5-甲基胞嘧啶被完全删除，但没有检测到该区域的易位或表达。另一个克隆编码一个类似Xa21的蛋白，Xa2lG。在野生型植物中，所有的胞嘧啶都在启动子区域内甲基化，而在Line-2中，相应的甲基化在世代中被完全消除。野生型中未检测到Xa2lG的表达，而LINE-2中Xa2lG呈结构性表达。当感染稻瘟病菌时。对Xa21以基因对基因方式赋予抗性的水稻，Line-2后代表现明显的抗性，而野生型则高度敏感而不表达Xa2lG。结论这些结果表明，Line-2中的去甲基化是选择性的，启动子去甲基化取消了Xa2lG高甲基化导致的结构性沉默，从而获得了抗病。低甲基化和抗性性状均稳定遗传。这是表观遗传的一个明显例子，支持拉马克遗传的观点，即后天性状是可遗传的。
Background and Aims Epigenetics is defined as mechanisms that regulate gene expression without base sequence alteration. One molecular basis is considered to be DNA cytosine methylation, which reversibly modifies DNA or chromatin structures. Although its correlation with epigenetic inheritance over generations has been circumstantially shown, evidence at the gene level has been limited. The present study aims to find genes whose methylation status directly correlates with inheritance of phenotypic changes.Methods DNA methylation in vivo was artificially reduced by treating rice (Oryza sativa ssp. japonica) seeds with 5-azadeoxycytidine, and the progeny were cultivated in the field for > 10 years. Genomic regions with changed methylation status were screened by the methylation-sensitive amplified polymorphysm, (MSAP) method, and cytosine methylation was directly scanned by the bisulfite mapping method. Pathogen infection with Xanthomonas oryzae pv. oryzae, race PR2 was performed by the scissors-dip method on mature leaf blades.Key Results The majority of seedlings were lethal, but some survived to maturity. One line designated as Line-2 showed a clear marker phenotype of dwarfism, which was stably inherited by the progeny over nine generations. MSAP screening identified six fragments, among which two were further characterized by DNA blot hybridization and direct methylation mapping. One clone encoding a retrotransposon gag-pol polyprotein showed a complete erasure of 5-methylcytosines in Line-2, but neither translocation nor expression of this region was detectable. The other clone encoded an Xa21-like protein, Xa2lG. In wild-type plants, all cytosines were methylated within the promoter region, whereas in Line-2, corresponding methylation was completely erased throughout generations. Expression of Xa2lG was not detectable in wild type but was constitutive in Line-2. When infected with X. oryzae pv. oryzae, against which Xa21 confers resistance in a gene-for-gene manner, the progeny of Line-2 were apparently resistant while the wild type was highly susceptible without Xa2lG expression.Conclusions These results indicated that demethylation was selective in Line-2, and that promoter demethylation abolished the constitutive silencing of Xa2lG due to hypermethylation, resulting in acquisition of disease resistance. Both hypomethylation and resistant trait were stably inherited. This is a clear example of epigenetic inheritance, and supports the idea of Lamarckian inheritance which suggested acquired traits to be heritable.