基于组学的柑橘砧木同源四倍体变异特征及其耐胁迫性评价

Polyploids are of great importance in scion and rootstock breeding of fruit trees. Phenotypic variations induced by polyploidy, especially the biomass and wide adaptability, make polyploids better adapted to environment or more suitable for agricultural production. Based on the potential value of polyploids in dwarfing and stress tolerance citrus rootstock improvement, the applicant has created plenty of citrus autotetraploid rootstocks in recent years, and these polyploids have flowered and set fruits. In this proposal, four typical autotetraploid rootstocks (i. e. trifoliate orange (Poncirus trifoliata（L.）Raf.); precocious trifoliate orange; red tangerine (Citrus reticulata Blanco); Ziyang xiangcheng (Citrus junos Sieb. ex Tanaka)) and their corresponding diploids will be used for integrated analysis by metabolome (LC-MS and GC-MS), transcriptome (RNA-Seq) and methylome (BS-Seq), and the metabolic, transcriptional and epigenetic consequences of autotetraploidization are expected to be revealed. The stress tolerance of the 4x and 2x rootstocks via drought and salt treatments and the mechanisms involved in the stress tolerance difference induced by autotetraploidization will also be investigated at morphological, physiological, metabolic and transcriptional levels. Based on previous strong research and special experimental materials, the implementation of this project is expected to enrich the theories of polyploidization in higher plants and provide strong theoretical basis for dwarfing and wide tolerance polyploid rootstock breeding in citrus.

多倍体在果树接穗和砧木育种中具有重要的应用价值。多倍体在形成过程中常产生新的表型，使其更适合自身或农业生产的需要；其中最突出的就是生物量和适应性的变化。基于多倍体在矮化、广适应性柑橘砧木育种中的潜在价值，申请人近年来发掘和创制了一批柑橘砧木类型的同源四倍体且已陆续开花结果。本项目拟以4对不同倍性的砧木类型（同源四倍体的枳、早实枳、红橘、香橙及其相应的二倍体）为试材，采用代谢组（GC-MS和LC-MS）、转录组（RNA-Seq）和甲基化组（BS-Seq）等技术，研究揭示砧木同源四倍体的形态、代谢、基因表达和表观修饰等变异特征；同时通过干旱和盐胁迫处理评价其耐胁迫能力，从形态生理、代谢物积累、基因表达等层面探讨其抗性差异的机制。本项目的前期基础扎实，试材独特；其实施将丰富植物多倍体化有关理论，为培育和筛选具有矮化、适应性广的柑橘多倍体砧木提供理论支撑。

柑橘双二倍体（同源四倍体）在广适应性砧木育种中具有重要的潜在价值。本项目以4对不同倍性的柑橘砧木类型为试材，其叶片DNA甲基化、small RNA和lnc RNA分析表明，二倍体及其同源四倍体在转录水平差异有限，多倍体化引起的叶片形态变化可能与植物信号转导过程相关；同源四倍体甲基化水平高于二倍体，且多数mC位点分布在基因间区，其次是TE区；且两组材料差异甲基化区域（DMR）分布存在差异。供试同源四倍体与二倍体的生理评价以及根尖转录组和代谢组分析表明，约5%基因在四倍体和二倍体间差异表达，上调基因主要富集到初生代谢通路，下调基因富集到次生（苯丙烷）代谢通路，与叶片代谢组分析基本吻合，即同源四倍体化促进初生代谢物积累，抑制次生代谢物积累；四倍体根系有机酸分泌量大于二倍体，使铝离子摄入减少，从而减轻铝毒害，增强铝胁迫耐性；四倍体较二倍体更耐盐胁迫，盐处理后四倍体ACO1和ERF基因表达量显著高于二倍体，说明四倍体可能通过提高ACO1和ERF表达量增强盐胁迫耐性；ERF基因可以结合ACO1基因启动子并增强其表达，超表达ACO1可以显著增强柑橘砧木耐盐性。本项目揭示了同源四倍体更耐胁迫的生理和分子基础，同时表明表观修饰在调控多倍体化引起的表型变异方面可能起着重要作用，为培育广适应性的柑橘多倍体砧木提供了理论依据。在Metabolomics、Plant Science、园艺学报等刊物发表论文4篇；培养毕业博士生1人、硕士生4人。