Liu Junxiang, Sun Chao, Zhai Fei-Fei, Li Zhenjian, Qian Yongqiang, Gu Lin, Sun Zhenyuan
State Key Laboratory of Tree Genetics and Breeding, Key Laboratory of Tree Breeding and Cultivation of the State Forestry and Grassland Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, P.R. China.
School of Architectural and Artistic Design, Henan Polytechnic University, Jiaozuo, Henan 454000, P.R. China.
Tree Physiol. 2021 Nov 8;41(11):2142-2152. doi: 10.1093/treephys/tpab055.
Bark chloroplasts play important roles in carbon balancing by recycling internal stem CO2 into assimilated carbon. The photosynthetic response of bark chloroplasts to interior stem environments has been studied recently in woody plants. However, the molecular regulatory mechanisms underlying specific characteristics of bark photosynthesis remain unclear. To address this knowledge gap, differences in the structure, photosynthetic activity and protein expression profiles between bark and leaf chloroplasts were investigated in Salix matsudana in this study. Bark chloroplasts exhibited broader and lower grana stacks and higher levels of starch relative to leaf chloroplasts. Concomitantly, decreased oxygen evolution rates and decreased saturated radiation point were observed in bark chloroplasts. Furthermore, a total of 293 differentially expressed proteins (DEPs) were identified in bark and leaf chloroplast profile comparisons. These DEPs were significantly enriched in photosynthesis-related biological processes or Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways associated with photosynthesis. All 116 DEPs within the KEGG pathways associated with photosynthesis light reactions were downregulated in bark chloroplasts, including key proteins responsible for chlorophyll synthesis, light energy harvesting, nonphotochemical quenching, linear electron transport and photophosphorylation. Interestingly, seven upregulated proteins involved in dark reactions were identified in bark chloroplasts that comprised two kinds of malic enzymes typical of C4-type photosynthesis. These results provide comprehensive proteomic evidence to understand the low photochemical capability of bark chloroplasts and suggest that bark chloroplasts might fix CO2 derived from malate decarboxylation.
树皮叶绿体通过将内部茎干中的二氧化碳循环转化为同化碳，在碳平衡中发挥着重要作用。最近在木本植物中研究了树皮叶绿体对内部茎干环境的光合响应。然而，树皮光合作用特定特征背后的分子调控机制仍不清楚。为了填补这一知识空白，本研究在旱柳中研究了树皮叶绿体和叶片叶绿体在结构、光合活性和蛋白质表达谱方面的差异。相对于叶片叶绿体，树皮叶绿体呈现出更宽、更低的基粒堆叠以及更高水平的淀粉。同时，在树皮叶绿体中观察到氧气释放速率降低和饱和辐射点降低。此外，在树皮和叶片叶绿体图谱比较中总共鉴定出293个差异表达蛋白（DEPs）。这些DEPs在与光合作用相关的生物过程或京都基因与基因组百科全书（KEGG）光合作用途径中显著富集。与光合作用光反应相关的KEGG途径中的所有116个DEPs在树皮叶绿体中均下调，包括负责叶绿素合成、光能捕获、非光化学猝灭、线性电子传递和光合磷酸化的关键蛋白。有趣的是，在树皮叶绿体中鉴定出7个参与暗反应的上调蛋白，其中包括两种典型的C4型光合作用苹果酸酶。这些结果为理解树皮叶绿体的低光化学能力提供了全面的蛋白质组学证据，并表明树皮叶绿体可能固定来自苹果酸脱羧的二氧化碳。
