毛白杨木质部单糖合成的遗传结构检测及关键调控位点的功能解析

Monosaccharides is the most abundant chemical composition of wood, which is the critical factor in affecting wood properties of trees. Thus, dissection of the genetic architecture and the molecular mechanism of key genetic factors for monosaccharide biosynthesis in perennial woody plants will significantly facilitate the genetic improvement of wood property traits in trees. Here, based on the germplasm resources of Populus tomentosa (435 unrelated individuals), four research topics will be carried out in this project: (1) Analysis of the phenotypic variations and population differentiation of xylem monosaccharide compositions in P. tomentosa; (2) Dissection of the additive, dominant, and epistatic effects of significant loci affecting the xylem monosaccharide biosynthesis using GWAS (genome-wide association study); (3) Deciphering of the genetic effects of candidate genetic factors at the transcriptional level by eQTN (expression quantitative trait nucleotide) mapping; (4) Validation of the molecular regulatory mechanisms of key genetic factors for monosaccharide biosynthesis using over-expression and CRISPR/Cas9 techniques. The study is supposed to uncover the genetic architecture of xylem monosaccharide biosynthesis in trees, identify the regulatory mechanism of key genetic factors, and develop the important regulatory pathway involving monosaccharide composition for wood property traits. It also provides an important model for dissecting the genetic basis of complex quantitative traits in trees, and promoting the development of tree breeding by molecular design.

单糖作为木材的主要化学成分，是影响林木木材品质性状的关键因素。因此，系统解析林木木质部单糖组分的遗传结构，揭示关键遗传因子调控木质部单糖合成的生物学功能，是林木木材品质性状遗传改良的基础。本项目以毛白杨种质资源（435株个体）为材料，系统开展：（1）毛白杨木质部单糖组分的群体遗传变异研究；（2）利用GWAS分析策略解析与木质部单糖合成显著连锁的SNPs的加性、显性与上位性遗传效应；（3）通过eQTN作图方法剖析关键遗传调控位点在转录水平的遗传效应；（4）利用过表达与CRISPR/Cas9等遗传转化体系鉴定关键遗传因子调控木质部单糖合成的分子机制。研究结果将揭示毛白杨木质部单糖合成的遗传结构，阐明关键遗传因子影响木质部单糖合成的分子机制，构建单糖合成影响木材品质性状的重要调控通路。本研究为解析林木复杂性状的遗传结构提供模式系统，对推动林木分子设计育种技术体系的建立，具有重要科学及应用价值。

作为木材化学组成的关键底物，细胞壁单糖组分是木材品质性状遗传改良的重要靶标。然而，树木木质部单糖组分的遗传构成尚不清晰，关键基因协同调控木质部单糖合成的分子机制有待深入研究。为此，本研究基于毛白杨种质资源群体，测定了木质部主要单糖含量，确定了阿拉伯糖、葡萄糖、木糖、甘露糖以及半乳糖是毛白杨木质部主要单糖类型，发现了毛白杨种质资源群体木质部主要单糖含量与化学组分存在丰富的表型变异。基于群体全基因组重测序数据，利用全基因组关联分析策略（Genome-wide association study，GWAS），系统解析了毛白杨木质部单糖组分与重要化学品质性状的遗传构成，共鉴定到132个SNP与8种性状显著关联（P < 5.07E-07，Bonferroni correction，P = 1/n），每一位点可解释表型变异率的1.29~19.23%；基因注释鉴定了58个蛋白编码基因与43个lncRNA，其通过多个生物学通路参与杨树单糖含量与木材品质性状的调控，发现了基因型组合模块对杨树木材品质性状具有更大的遗传效应。为深入剖析关键基因的分子作用机制，本研究重点关注了多效性基因PtoMYB62与PtoMYB80，发现了PtoMYB62与PtoMYB80对于其所关联的性状表现出了相同或相反的遗传效应模式，并联合利用eQTN作图与共表达调控网络分析，鉴定了PtoMYB62与PtoMYB80潜在的转录调控网络。基于构建的PtoMYB62与PtoMYB80过表达与CRISPR/Cas9基因敲除株系，发现了PP2C39-MYB62-XET6/LAC3通路通过正向调控木糖含量与木质素含量协同影响木材品质性状；PBL37-MYB80-UCH3/GAP通路通过提高木糖含量、降低葡萄糖含量共同调控杨树木材品质性状。上述研究结果首次在群体水平揭示了木材单糖组分的遗传学基础，为木材品质性状的遗传改良与林木分子育种提供了重要的理论基础与技术支撑。