基于单细胞ATAC-seq技术的C4光合调控分子机制研究

大部分植物的C3光合作用发生在叶肉细胞。为适应恶劣环境一些被子植物进化出更有效的C4光合。它们在叶肉细胞内完成碳的固定，随后在维管束鞘细胞中经过脱羧反应释放CO2给卡尔文循环。细胞分工是C4的关键，将光合基因差异表达于两种细胞是分子基础。依据脱羧酶的种类C4植物可被划分为三种亚型：NAD-ME、NADP-ME和PEPCK。我们前期研究发现玉米和高粱等NADP-ME型C4植物的基因表达受启动子染色质开放性影响。为更好地研究C4谱系中染色质开放性图谱的差异，我们自主开发了一种单细胞组合标记ATAC-seq测序技术，首先成功分析了7281个玉米叶片单细胞，阐明4个细胞亚群的调控差异。本项目希望以玉米、小米和棕顶臂型草为C4亚型代表，通过此技术结合比较基因组学，探究物种间调控机制差异。这项对C4光合趋同进化的分析研究，将有助于我们揭示驱动C4光合的关键因子，为C3植物C4改造工程提供新思路。

Unlike the C3 plants which complete the photosynthesis in a single cell type, C4 plants fixed CO2 into a C4 acids in mesophyll cell. It is then transported into the bundle sheath cells where it converted back to CO2 and takes part in the Calvin cycle. C4 photosynthesis is a remarkable example of convergent evolution, which is associated with morphological adaptation as well as the strict compartmentation of biochemical activities two cell types. C4 plants can be further classified into three subtypes based on the primary decarboxylating enzyme: NADP malic enzyme (NADP-ME), NAD malic enzyme (NAD-ME) and phosphoenolpyruvate carboxykinase (PCK). The decarboxylation in the bundle sheath cells can occur in distinct cellular compartments, since NADP-ME occurs in chloroplasts, NAD-ME in mitochondria, whereas PEPCK exhibits cytosolic activity. Our previous studies revealed that the maize cell-specific C4 photosynthesis genes could be regulated by promoter open chromatin changes. In this study, I propose to use single-cell combinatorial index ATAC-seq technologies to profile the genome-wide chromatin landscape in three C4 subtype model grasses: maize (NADP-ME), proso millet (NAD-ME) and browntop signalgrass. Comparative genomic analysis will be performed to study the regulatory mechanisms. This cross-species multi-omics analysis of the C4 plants will shed light on the genetic mechanisms driving C4 evolution and provide new direction for engineering C4 traits into C3 crops.