基于LTR类反转座子的天门冬属植物性染色体起源及演化的分子细胞学路径解析

进化理论表明性染色体起源于一对常染色体，但是从常染色体到性染色体演化所经历的分子细胞学路径至今仍不清楚。百合科天门冬属既包含雌雄异株植物，也包含两性花植物，全属染色体基数相同，且其雌雄异株模式植物石刁柏全基因组测序已完成，故该属是追踪植物性染色体起源及演化路径的理想材料。前期我们对该属8种雌雄异株和3种两性花植物进行了低深度基因组测序，数据分析表明LTR类反转座子可能在该属性染色体演化过程中起重要作用。在此基础上，本项目拟采用比较基因组学、FISH、免疫荧光等技术，通过对LTR类反转座子在雌雄异株种性染色体及两性花种相对应染色体上分布模式和扩增特征、性染色体LTR类反转座子插入时间、重排特征及其激发性染色体异染色质化机制等问题进行系统的比较研究，旨在解析天门冬属植物性染色体起源及演化的分子细胞学路径。研究结果将对揭示植物性染色体演化乃至动物性染色体早期起源及演化之谜提供重要的理论依据。

Evolutionary theory demonstrates that sex chromosomes originated from a pair of autosomes. However, the molecular cytogenetic route of the sex chromosome evolution from autosome is still not clear. The genus Asparagus (Liliaceae) contains a large number of dioecious and hermaphrodite plants, and the chromosome base number of this genus is identical. Furthermore, the genome of the model dioecious plant of this genus, Asparagus officinalis, has been sequenced. Thus, this genus is an ideal material for tracing the route of sex chromosome origin and evolution in plants. Previously, we have sequenced 11 Asparagus plants, including 8 dioecious and 3 hermaphrodite plants, using low depth sequencing. Preliminary analysis indicated that LTR retrotransposons might play important roles in sex chromosome evolution in Asparagus. Based on these results, we will use a combination of comparative genomics, FISH, and immunofluorescence techniques to analyze the distribution pattern and proliferation feature of different types of LTR retrotransposons in the sex chromosomes of dioecious plants and the corresponding chromosomes of hetermaphrodite plants, to analyze the insetion time of LTR retrotransposons in the sex chromosomes, and to study the distribution and rearrangement feature of LTR retrotransposons in Asparagus sex chromosomes. Furthermore, we will explore the mechanism of the sex chromosome heterochromatization stimulated by LTR retrotransposons in Asparagus plants. Through these analyses, we intend to investigate the possible molecular and cellular route of sex chromosome origin and evolution in Asparagus. The expected data and results will have guiding theoretical significance for investigation of the molecular and cellular mechanism of sex chromosome evolution in plants, even of sex chromosome origin and early evolution in animal kingdom.