光受体及信号转导元件在光照调控桃果实着色及品种间对光敏感性差异中的作用及其机制

Anthocyanins are important compounds affecting fruit quality, and fruit color can be improved through increasing the anthocyanin accumulation. Anthocyanins are pigments accumulated in ripe peach fruit, and its accumulation can be enhanced by light through stimulating the expression of transcription factors MYB, bHLH and WD40, as revealed by our previous studies. However, how the expression of transcription factors was regulated by light remains to be a mystery. Meanwhile, the mechanisms underlying the different sensitivity to light among cultivars were unexplored. With “Hujingmilu”, “Yulu”, and “Late Hujingmilu” peach as material, and by applying functional genomics, molecular and biotechnological techniques, this project focuses on the functional characterization of genes encoding light receptors, including UV-B receptor UVR8 as well as UV-A/blue light receptor Cry1 and Cry2, and signaling elements like COP1 and HY5, etc., and their roles and the mechanisms involved in regulation of MYB, bHLH and WD40. By comparing differences in gene sequence and gene expression, and analyzing transcriptional regulation and protein interaction details, the project aimed to answer why the anthocyanin accumulation in peach was light dependent and why the anthocyanin biosynthesis and its sensitivity to light varies among cultivars. The study can contribute to elucidation of the mechanisms of anthocyanin biosynthesis and its regulation, as well as to provide a basis for exploring strategies for improving accumulation of anthocyanins in peach fruit.

花色苷是果实品质重要因子，提高果实花色苷含量可改进果实色泽。桃为积累花色苷的重要水果，先前研究已经表明光可通过增强相关转录因子（MYB、bHLH 和 WD40）基因表达而促进花色苷合成，但光照如何实现对转录因子基因表达的调控尚不清楚，而且就品种间对光存在敏感性差异的成因尚无研究。本项目拟以‘湖景蜜露’、‘玉露’和‘晚湖景’桃为研究材料，结合运用功能基因组学、分子生物学和生物技术等手段，以光受体（UV-B受体UVR8、UV-A/蓝光受体Cry1、Cry2）及信号转导中的元件（COP1、HY5等）功能鉴别及其对MYB、bHLH 和 WD40的作用机制等为主题，从基因序列差异、基因表达差异、转录调控途径和蛋白互作机制等角度入手，研究桃果实着色对光的依赖机制以及品种间对光敏感性存在差异的成因。项目研究对于深入理解桃果实花色苷的积累及调控机制具有重要意义，也可为探索提高花色苷含量的措施提供理论支撑。

以自然光下着色能力较强的‘湖景蜜露’和着色能力较弱的‘玉露’桃果实为试材，探究了不同光环境下花色苷积累差异机制以及品种间紫外光敏感性差异的成因。主要研究进展包括：1）发现在自然光下‘湖景蜜露’随着果实的成熟逐渐积累花色苷，而‘玉露’几乎未积累花色苷。为探究两个桃品种花色苷积累的差异是否由于合成及调控基因序列差异导致，开展了以高通量测序为基础的品种间单核苷酸多态性（SNP）筛选，发现只有UFGT由于SNP位点的差异造成了2个氨基酸残基的差异但这些差异很可能并不会导致活性上的影响。2）发现采后光照处理下两个品种对不同波长的光具有不同的敏感性。UVB和UVA照射显著增加了‘湖景蜜露’果皮中花色苷含量，‘玉露’仅在UVB处理下积累花色苷。转录组数据表明花色苷生物合成结构基因表达量与花色苷含量变化一致。一些光受体（PpUVR8.1和PpCRY1）、光信号转导因子（PpCOP1、PpCOP10和PpHY5、PpHYH）以及花色苷转运基因（PpGST1）是两个品种桃对紫外光敏感性差异的原因。研究发现MYB、bHLH、bZIP和NAC家族中的一些转录因子与花色苷结构基因共表达，可能参与紫外光调控桃果实花色苷的合成。3）通过转录组分析鉴定出参与花色苷转运的GST基因（PpGST1），PpGST1表达量存在组织和品种特异性，与花色苷含量显著正相关。基于拟南芥突变体功能互补及烟草和桃果实瞬时过表达实验表明PpGST1能参与花色苷的转运，而未参与原花青素的积累。在血桃中用VIGS技术将PpGST1沉默后，果肉中花色苷的含量明显减少。R2R3-MYB转录因子PpMYB10.1不仅调控花色苷的生物合成，而且能通过激活PpGST1的表达，协同调控桃果实发育成熟过程中花色苷的转运过程。研究探明了光照处理促进花青苷积累的效应、品种间差异及其机制，鉴别了HY5和GST等重要基因，对产业上调控果实着色提供了理论支撑。