杨树全同胞异源异倍性群体表型变异及遗传调控机制研究

Chromosome number variation with polyploidization and aneuploidization always leads to extensive phenotypic changes because of the disturbed genomic dosage balance, which is widely used in studies of genetics and improvement of plants. However, effect of different types of chromosome number variation and karyotypic construction for formation of important traits and its molecular mechanism remain poorly understood in woody plants, owing to lack of suitable materials for study. We have produced a full-sib allo-heteroploidy population, with kinds of chromosome number variation types and obvious phenotypic variation, by interploidy cross between diploid female parent P. tomentosa × P. bolleana 'Maoxin' and triploid male parent P. alba × P. berolinensis 'Yinzhong' in the previous study, which makes it possible to understand this scientific issue. In this project, the types of chromosomal number variation and karyotypic construction will be analyzed based on this population, combining with phenotypic measurements, genomic structure and heterozygosity analysis, DNA methylation alterations and expression patterns of differently methylated genes, to investigate the following subjects: (1) Pattern of chromosomal number variation and feature of chromosomal composition in offspring of the interploidy cross; (2) Relationship between phenotypic characteristics and chromosomal number variation and karyotypic construction; (3) Interactional relation between genomic heterozygous effect and dosage imbalance and its genetic regulatory mechanism for phenotypic variation of Populus. The conduct of this project will develop the theoretical basis on chromosome engineering breeding of trees and make a foundation for establishment of strategies on sexual utilization of allo-polyploids and aneuploid breeding of Populus.

多倍性和非整倍性染色体数目变异由于打破了基因组剂量的平衡，往往造成丰富的表型变化，在植物遗传改良研究中广泛利用。然而，由于研究材料的限制，有关木本植物不同染色体数目变异类型及核型构成对重要性状形成的影响及分子机制尚不明确。我们前期通过二倍体'毛新杨'×三倍体'银中杨'构建的全同胞异源异倍性群体，染色体数目变异类型丰富，表型变异明显，为相关科学问题的阐明提供了可能。本项目基于该群体材料，开展染色体数目变异及核型分析，结合表型测量、基因组结构及杂合性分析、DNA甲基化变异及甲基化差异基因表达模式等研究，来探讨（1）杨树异倍体杂交子代的染色体数目变异模式及染色体组成特点；（2）染色体数目变异和核型构成与表型变异的关系；（3）基因组杂合效应与剂量不平衡的互作关系及其对杨树表型变异的遗传调控机制。从而深化林木染色体工程定向育种理论基础，为杨树异源多倍体有性利用及非整倍体育种策略的制定提供依据。

染色体变异是造成植物表型变异的重要因素。本项目以二倍体‘毛新杨’与三倍体‘银中杨’异倍体杂交子代群体为研究材料，对其染色体组成和结构变异规律及其对表型变异的影响、基因组杂合性及父源杂合性传递规律、DNA甲基化变异模式等进行了研究。结果表明，异倍体杂交造成复杂的倍性分离，子代群体中不仅包括少量二倍体和四倍体，还包括大量的非整倍体植株。综合利用基于SSR毛细管电泳检测的分子核型分析方法和基于基因组重测序Read Count的染色体结构检测，明确了各子代个体的染色体组成和重复、缺失等结构变异的准确位置，发现其中存在大量亚三倍体、超三倍体、亚四倍体，甚至还有超四倍体植株存在，其具有5条Chr01、Chr05和/或Chr09。重复和缺失染色体结构变异在Chr01-Chr07和Chr13-Chr19的14条染色体上均有发现，且多发生于染色体端部（73.17%）。在检测到的重复和缺失结构变异中，染色体重复变异占36.59%，缺失变异占63.41%。经细胞学分析，我们认为四倍体子代的获得是由于‘银中杨’未减数花粉授粉的结果，重复和缺失等染色体结构变异的发生则可能是异常联会过程发生了错误交换的结果。表型分析发现，非整倍体植株生长性状总体处于劣势，但也存在少量生长较好的单株。初步分析发现非整倍植株中Chr03、Chr16、Chr19等染色体的剂量分别与其地径生长量呈显著正相关（P < 0.05），表明相关染色体的剂量变异对植株生长具有影响。而子代基因组杂合性水平与表型分化无显著相关，推测基因组杂合性与染色体剂量变异的互作可能对表型变异产生影响。MSAP分析发现异倍体杂交子代发生了去甲基化现象。此外，本研究还针对三倍体杨树配子高度败育的问题，提出了通过抑制其减数第一次分裂同源染色体分离提高配子育性的方法，并诱导了‘银中杨’六倍体新种质，为开展多倍体杨树的有性利用提供了借鉴。本项目研究增强了我们对林木染色体数目和结构变异遗传效应的理解，也为开展杨树染色体结构和功能分析提供了材料，为开展杨树染色体工程育种奠定了基础。