DataSheet_2_Reduction in chloroplastic ribulose-5-phosphate-3-epimerase decreases photosynthetic capacity in Arabidopsis.docx

Chloroplast ribulose-5-phosphate-3-epimerase (RPE) is a critical enzyme involved in the Calvin-Benson cycle and oxidative pentose phosphate pathways in higher plants. Three Arabidopsis rpe mutants with reduced level of RPE were identified through their high NPQ (nonphotochemical quenching) phenotype upon illumination, and no significant difference of plant size was found between these rpe mutants and WT (wild type) plants under growth chamber conditions. A decrease in RPE expression to a certain extent leads to a decrease in CO2 fixation, Vcmax and Jmax. Photosynthetic linear electron transport was partially inhibited and activity of ATP synthase was also decreased in the rpe mutants, but the levels of thylakoid protein complexes and other Calvin-Benson cycle enzymes in rpe mutants were not affected. These results demonstrate that some degree of reduction in RPE expression decreases carbon fixation in chloroplasts, which in turn feedback inhibits photosynthetic electron transport and ATP synthase activity due to the photosynthetic control. Taken together, this work provides evidence that RPE plays an important role in the Calvin-Benson cycle and influences the photosynthetic capacity of chloroplasts.

叶绿体核酮糖-1,5-二磷酸-3-差向异构酶（RPE）是高等植物卡尔文-本森循环和氧化型戊糖磷酸途径中的一种关键酶。通过光照条件下表现出的高非光化学猝灭（NPQ）表型，鉴定了三种拟南芥rpe突变体，其RPE水平降低。在生长室条件下，这些rpe突变体与野生型（WT）植物在植物大小上未发现显著差异。RPE表达的降低在一定程度上导致二氧化碳固定、最大羧化速率（Vcmax）和最大光合速率（Jmax）的下降。光合线性电子传递部分受到抑制，且rpe突变体中ATP合酶的活性也降低。然而，rpe突变体中类囊体蛋白复合物和其他卡尔文-本森循环酶的水平并未受到影响。这些结果表明，RPE表达程度的降低在一定程度上减少了叶绿体中的碳固定，进而由于光合控制反馈抑制了光合电子传递和ATP合酶的活性。综上所述，这项研究为RPE在卡尔文-本森循环中的重要作用及其对叶绿体光合能力的影响提供了证据。