Puthiyaveetil Sujith, Woodiwiss Timothy, Knoerdel Ryan, Zia Ahmad, Wood Magnus, Hoehner Ricarda, Kirchhoff Helmut
Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340, USA.
Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340, USA
Plant Cell Physiol. 2014 Jul;55(7):1245-54. doi: 10.1093/pcp/pcu062. Epub 2014 May 3.
PSII undergoes photodamage, which results in photoinhibition-the light-induced loss of photosynthetic activity. The main target of damage in PSII is the reaction center protein D1, which is buried in the massive 1.4 MDa PSII holocomplex. Plants have evolved a PSII repair cycle that degrades the damaged D1 subunit and replaces it with a newly synthesized copy. PSII core proteins, including D1, are phosphorylated in high light. This phosphorylation is important for the mobilization of photoinhibited PSII from stacked grana thylakoids to the repair machinery in distant unstacked stroma lamellae. It has been recognized that the degradation of the damaged D1 is more efficient after its dephosphorylation by a protein phosphatase. Recently a protein phosphatase 2C (PP2C)-type PSII core phosphatase (PBCP) has been discovered, which is involved in the dephosphorylation of PSII core proteins. Its role in PSII repair, however, is unknown. Using a range of spectroscopic and biochemical techniques, we report that the inactivation of the PBCP gene affects the growth characteristic of plants, with a decreased biomass and altered PSII functionality. PBCP mutants show increased phosphorylation of core subunits in dark and photoinhibitory conditions and a diminished degradation of the D1 subunit. Our results on D1 turnover in PBCP mutants suggest that dephosphorylation of PSII subunits is required for efficient D1 degradation.
光系统II（PSII）会遭受光损伤，这会导致光抑制——即光诱导的光合活性丧失。PSII中损伤的主要靶点是反应中心蛋白D1，它埋藏在巨大的1.4兆道尔顿的PSII全复合物中。植物进化出了一个PSII修复循环，该循环会降解受损的D1亚基，并用新合成的拷贝取而代之。包括D1在内的PSII核心蛋白在高光条件下会被磷酸化。这种磷酸化对于将光抑制的PSII从堆叠的基粒类囊体转移到远处未堆叠的基质类囊体中的修复机制至关重要。人们已经认识到，受损的D1在被一种蛋白磷酸酶去磷酸化后，其降解效率更高。最近发现了一种蛋白磷酸酶2C（PP2C）型的PSII核心磷酸酶（PBCP），它参与PSII核心蛋白的去磷酸化过程。然而，其在PSII修复中的作用尚不清楚。我们使用一系列光谱和生化技术报告称，PBCP基因的失活会影响植物的生长特性，导致生物量减少和PSII功能改变。PBCP突变体在黑暗和光抑制条件下显示核心亚基的磷酸化增加，且D1亚基的降解减少。我们关于PBCP突变体中D1周转的结果表明，PSII亚基的去磷酸化是D1有效降解所必需的。
