Mutation in the tropical tree canopy

Genetic diversity is an essential prerequisite for the capacity of all life to adapt to an ever-changing environment, and trees are notorious for their large standing genetic variation. There are several ways by which genetic variation can be incorporated or reshuffled in a species, but the only way of generating truly novel genetic diversity is through mutation. Scientists have dedicated considerable efforts to understand the roles of phylogeography, local adaptation, speciation, and hybridisation in modulating genetic diversity of tropical trees, however, our current knowledge of mutational processes in tropical trees is very limited. Recent advances in DNA sequencing techniques now allow us to detect single point mutations with unprecedented precision, which opens up exciting possibilities in mutation research. We propose to sequence the genomes of tropical rainforest trees in French Guiana, providing, for the first time, reference genomes of three Neotropical rainforest tree species. We will test intra-individual and inter-specific effects of low to extreme canopy sunlight exposure on the accumulation of novel mutations. The tree architecture (i.e., the branching pattern) will represent the null hypothesis for the pattern of accumulation of mutations. We will test the existence of a soma vs. germline segregation in tropical trees and the transmission of novel mutations from parent to offspring. The genomic data and knowledge to be generated in the project represent crucial information towards understanding genome evolution and its drivers in long-lived organisms. The comparison of mutational processes among tropical species, combined with the potential retention of mutations in offspring should be invaluable in assessing the importance of mutation rates in the creation and maintenance of Neotropical diversity.遗传多样性（genetic diversity）是所有生命适应不断变化环境的核心前提，而树木素来以其丰富的固有遗传变异著称。物种可通过多种途径整合或重排遗传变异，但唯有突变能够产生真正全新的遗传多样性。科学家已投入大量精力，探究系统地理学（phylogeography）、局部适应、物种形成以及杂交（hybridisation）在调控热带树木遗传多样性中的作用，但目前学界对热带树木突变过程的认知仍十分有限。近年来DNA测序技术的进步，使我们能够以前所未有的精度检测单点突变（single point mutation），这为突变研究带来了令人振奋的全新可能。本研究计划对法属圭亚那（French Guiana）的热带雨林树木基因组进行测序，首次获取三种新热带区（Neotropical）热带雨林树种的参考基因组（reference genome）。我们将探究从低到极端冠层光照暴露条件下，个体内与种间的新突变积累效应。树木的构型（即分枝模式）将作为突变积累模式的零假设（null hypothesis）参照基准。我们将验证热带树木中体细胞（soma）与生殖系（germline）分离现象是否存在，并解析新突变从亲本向子代的传递过程。本项目产出的基因组数据与相关研究认知，将为理解长寿命生物的基因组演化及其驱动因子提供关键依据。对热带树种间突变过程的比较研究，结合突变在子代中的潜在保留情况，将为评估突变率在新热带区生物多样性的产生与维持中的重要性提供极为宝贵的参考价值。