Department of Botany, Graduate School of Science, Kyoto University, Kyoto, 606-8502 Japan.
Plant Cell Physiol. 2013 Sep;54(9):1525-34. doi: 10.1093/pcp/pct098. Epub 2013 Jul 19.
In Arabidopsis thaliana, the main route of cyclic electron transport around PSI is sensitive to antimycin A, but the site of inhibition has not been clarified. We discovered that ferredoxin-dependent plastoquinone reduction in ruptured chloroplasts was less sensitive to antimycin A in Arabidopsis that overaccumulated PGR5 (PROTON GRADIENT REGULATION 5) originating from Pinus taeda (PtPGR5) than that in the wild type. Consistent with this in vitro observation, infiltration of antimycin A reduced PSII yields and the non-photochemical quenching (NPQ) of Chl fluorescence in wild-type leaves but not in leaves accumulating PtPGR5. There are eight amino acid differences between PGR5 of Arabidopsis (AtPGR5) and PtPGR5 in their mature forms. To determine the site conferring antimycin A resistance, a series of AtPGR5 and PtPGR5 variants was introduced into the Arabidopsis pgr5 mutant. We determined that the presence of lysine rather than valine at the third amino acid position was necessary and sufficient for resistance to antimycin A. High levels of resistance to antimycin A required overaccumulation of PtPGR5 in ruptured chloroplasts, suggesting that PtPGR5 is partly resistant to antimycin A. In contrast, PSII yield was almost fully resistant to antimycin A in leaves accumulating endogenous levels of PtPGR5 or AtPGR5 V3K that had lysine instead of valine at the third position. NPQ was also dramatically recovered in leaves of these lines. These results imply that partial recovery of PSI cyclic electron transport is sufficient for maintaining redox homeostasis in photosynthesis. Our discovery suggests that antimycin A inhibits the function of PGR5 or proteins localized close to PGR5.
在拟南芥中，PSI 周围环式电子传递的主要途径对antimycin A 敏感，但抑制部位尚未阐明。我们发现，拟南芥中超积累来自火炬松（PtPGR5）的 PROTON GRADIENT REGULATION 5（PGR5）（PtPGR5）的断裂叶绿体中依赖于铁氧还蛋白的质体醌还原对 antimycin A 的敏感性低于野生型。与体外观察一致，antimycin A 的渗透降低了野生型叶片中 PSII 的产量和叶绿素荧光的非光化学猝灭（NPQ），但在积累 PtPGR5 的叶片中则没有。在它们的成熟形式中，拟南芥的 PGR5（AtPGR5）和 PtPGR5 之间有八个氨基酸差异。为了确定赋予 antimycin A 抗性的位点，一系列 AtPGR5 和 PtPGR5 变体被引入拟南芥 pgr5 突变体中。我们确定，第三个氨基酸位置上的赖氨酸而不是缬氨酸的存在是对 antimycin A 抗性的必要和充分条件。对 antimycin A 的高抗性需要在断裂的叶绿体中超积累 PtPGR5，表明 PtPGR5 部分对 antimycin A 有抗性。相比之下，在积累内源性水平的 PtPGR5 或 AtPGR5 V3K 的叶片中，PSII 的产量几乎完全对 antimycin A 具有抗性，这些突变体在第三个位置上具有赖氨酸而不是缬氨酸。这些品系的 NPQ 也得到了显著恢复。这些结果表明，PSI 环式电子传递的部分恢复足以维持光合作用中的氧化还原平衡。我们的发现表明，antimycin A 抑制了 PGR5 或定位于 PGR5 附近的蛋白质的功能。
