Institute of Low Temperature Science, Hokkaido University, N19 W8 Kita-Ku, Sapporo, 060-0819 Japan.
Plant Cell Physiol. 2011 Dec;52(12):2103-14. doi: 10.1093/pcp/pcr138. Epub 2011 Oct 17.
The reversible associations between the light-harvesting complexes (LHCs) and the core complexes of PSI and PSII are essential for the photoacclimation mechanisms in higher plants. Two types of Chls, Chl a and Chl b, both function in light harvesting and are required for the biogenesis of the photosystems. Chl b-less plants have been studied to determine the function of the LHCs because the Chl b deficiency has severe effects specific to the LHCs. Previous studies have shown that the amounts of the LHCs, especially the LHCII trimer, were decreased in the mutants; however, it is still unclear whether Chl b is required for the assembly of the LHCs and for the association of the LHCs with PSI and PSII. Here, to reveal the function of Chl b in the LHCs, we investigated the oligomeric states of the LHCs, PSI and PSII in the Arabidopsis Chl b-less mutant. A two-dimensional blue native-PAGE/SDS-PAGE demonstrated that the PSI-LHCI supercomplex was fully assembled in the absence of Chl b, whereas the trimeric LHCII and PSII-LHCII supercomplexes were not detected. The PSI-NAD(P)H dehydrogenase (NDH) supercomplexes were also assembled in the mutant. Furthermore, we detected two forms of monomeric LHC proteins. The faster migrating forms, which were detected primarily in the mutant, were probably apo-LHC proteins, whereas the slower migrating forms were probably the LHC proteins that contained Chl a. These findings increase our understanding of the Chl b function in the assembly of LHCs and the association of the LHCs with PSI, PSII and NDH.
在高等植物中，光捕获复合物（LHCs）与 PSI 和 PSII 的核心复合物之间的可逆关联对于光驯化机制是必不可少的。两种类型的 Chls，Chl a 和 Chl b，都具有光捕获功能，是光合作用系统生物发生所必需的。已经研究了 Chl b 缺失的植物，以确定 LHCs 的功能，因为 Chl b 的缺乏对 LHCs 有严重的特异性影响。先前的研究表明，在突变体中，LHCs 的数量减少，特别是 LHCII 三聚体；然而，目前尚不清楚 Chl b 是否需要用于 LHCs 的组装以及 LHCs 与 PSI 和 PSII 的关联。在这里，为了揭示 Chl b 在 LHCs 中的功能，我们研究了拟南芥 Chl b 缺失突变体中 LHCs、PSI 和 PSII 的寡聚状态。二维蓝色 native-PAGE/SDS-PAGE 表明，PSI-LHCI 超复合物在没有 Chl b 的情况下完全组装，而三聚体 LHCII 和 PSII-LHCII 超复合物则未检测到。PSI-NAD(P)H 脱氢酶（NDH）超复合物也在突变体中组装。此外，我们还检测到两种形式的单体 LHC 蛋白。在突变体中主要检测到的迁移速度较快的形式可能是apo-LHC 蛋白，而迁移速度较慢的形式可能是含有 Chl a 的 LHC 蛋白。这些发现增加了我们对 Chl b 在 LHCs 组装和 LHCs 与 PSI、PSII 和 NDH 关联中的功能的理解。
