The architecture of intra-organism mutation rate variation in plants

First author: Long Wang; Affiliations: Nanjing University (南京大学): Nanjing, China

Corresponding author: Dacheng Tian

Given the disposability of somatic tissue, selection can favor a higher mutation rate in the early segregating soma than in germline, as seen in some animals. Although in plants intra-organismic mutation rate heterogeneity is poorly resolved, the same selectionist logic can predict a lower rate in shoot than in root and in longer-lived terminal tissues (e.g., leaves) than in ontogenetically similar short-lived ones (e.g., petals), and that mutation rate heterogeneity should be deterministic with no significant differences between biological replicates. To address these expectations, we sequenced 754 genomes from various tissues of eight plant species. Consistent with a selectionist model, the rate of mutation accumulation per unit time in shoot apical meristem is lower than that in root apical tissues in perennials, in which a high proportion of mutations in shoots are themselves transmissible, but not in annuals, in which somatic mutations tend not to be transmissible. Similarly, the number of mutations accumulated in leaves is commonly lower than that within a petal of the same plant, and there is no more heterogeneity in accumulation rates between replicate branches than expected by chance. High mutation accumulation in runners of strawberry is, we argue, the exception that proves the rule, as mutation transmission patterns indicate that runner has a restricted germline. However, we also find that in vitro callus tissue has a higher mutation rate (per unit time) than the wild-grown comparator, suggesting nonadaptive mutational “fragility”. As mutational fragility does not obviously explain why the shoot—root difference varies with plant longevity, we conclude that some mutation rate variation between tissues is consistent with selectionist theory but that a mechanistic null of mutational fragility should be considered.

由于体细胞并不会遗传给下一代，所以选择会偏向于体细胞早期分离时的突变率高于生殖细胞，这种现象在某些动物中已经有过报道。尽管，目前对于植物个体内突变率的异质性所知不多，但我们可以通过同样的选择逻辑来预测茎中的突变率要低于根中的，存活时间更长的末端组织（如叶片）要低于形态发生来源类似但存活时间更短的末端组织（如花瓣），并且不同的生物学重复之间不应该存在显著的突变率异质性差异。为了验证这些期望是否属实，作者对来自8个植物物种的754不同组织进行了基因组测序。结果显示，在多年生植物物种中，单位时间内茎尖分生组织中积累的突变要少于根尖组织，而茎尖中的突变有很大一部分是可遗传的，这与一年生的植物不一样，一年生植物体细胞的变异更加倾向于不会遗传给下一代。与此类似，在叶片中积累的突变要比同一植物上花瓣中积累的突变少，并且重复之间的突变积累率并不存在显著差别。草莓走茎具有较高的突变积累，作者推测这可能是普遍规则的一个例外，因为突变遗传模式显示走茎中的突变并不会传递给走茎上新长出的植株。作者还发现了离体愈伤组织要比野生生长的对照具有更高的突变率，说明了非适应性的突变“脆弱性”。既然突变脆弱性并不能完全解释为何茎-根之间的差异随着植物寿命的不同存在变异，作者推测某些组织间的突变率差异与选择理论相一致，但也要考虑到不含突变脆弱性的机制的影响。

p.s. 这个翻译实在是太难了。。。（大家感兴趣的自行阅读原文吧，参考：http://life.nju.edu.cn/00/10/c12937a327696/page.htm）

通讯：田大成  (http://gattaca.nju.edu.cn/dachengcn.html)

个人简介：南京农业大学，博士；澳大利亚Newcastle大学，博士。

研究方向：植物抗病基因的结构、功能、起源、变异及保存；DNA insertion/deletion对遗传变异的影响；基因组的非对称性及其非对称DNA的遗传效应；肿瘤基因组体细胞突变的分子遗传机制。

doi: https://doi.org/10.1371/journal.pbio.3000191

Journal: PLOS Biology

Published date: April 09, 2019