Wu Fenghua, Li Xiuxiu, Yang Gongxian, Song Jince, Zhao Xiaoyu, Zhu Lixia, Qin Xiaochun
School of Biological Science and Technology, University of Jinan, Jinan, China.
School of Chemistry and Chemical Engineering, University of Jinan, Jinan, China.
Biochem Biophys Res Commun. 2022 Jul 5;612:77-83. doi: 10.1016/j.bbrc.2022.04.102. Epub 2022 Apr 25.
In higher plants, the PSI core complex is associated with light-harvesting complex I (LHCI), forming the PSI-LHCI super-complex. In vascular plants, four major antenna proteins (LHCA1-4) are assembled in the order of LHCA1, LHCA4, LHCA2, and LHCA3 into a crescent-shaped LHCI, while LHCA5 and LHCA6 are minor antenna proteins. By contrast, in moss and green algae, LHCA5 or LHCA5-like protein functions as one of the major antenna proteins by residing at the second site of LHCI. In order to learn the effect of binding different LHCA proteins, i.e. LHCA4 or LHCA5, within the PSI-LHCI super-complex on photosynthetic properties of plants, we constructed LHCA5 overexpression plants with a wild type (WT) background and an lhca4 mutant background in Arabidopsis thaliana. The results showed that: (i) there are little difference in phenotype, pigment composition and chlorophyll fluorescence parameters between the transgenic Arabidopsis and their corresponding background materials; (ii) in spite of a small amount of LHCA5, the LHCA5-included PSI-LHCI super-complex can be obtained by extracting samples incubated with anti-FLAG M2 Affinity Gel, in which LHCA5 is found to substitute for LHCA4 as analyzed by immunoblotting analysis; (iii) the replacement of LHCA4 with LHCA5 within PSI-LHCI super-complex leads to a blue shift in low temperature fluorescence emission, suggesting a decrease in far-red absorbance. These results provide new clues for understanding the position and function of LHCA4 and LHCA5 during the evolution of green plants from aquatic to terrestrial lifestyles.
在高等植物中，PSI核心复合体与光捕获复合体I（LHCI）相关联，形成PSI-LHCI超级复合体。在维管植物中，四种主要的天线蛋白（LHCA1-4）按照LHCA1、LHCA4、LHCA2和LHCA3的顺序组装成新月形的LHCI，而LHCA5和LHCA6是次要的天线蛋白。相比之下，在苔藓和绿藻中，LHCA5或LHCA5样蛋白通过位于LHCI的第二个位点而作为主要天线蛋白之一发挥作用。为了了解在PSI-LHCI超级复合体中结合不同的LHCA蛋白（即LHCA4或LHCA5）对植物光合特性的影响，我们在拟南芥中构建了具有野生型（WT）背景和lhca4突变体背景的LHCA5过表达植株。结果表明：（i）转基因拟南芥与其相应的背景材料在表型、色素组成和叶绿素荧光参数方面几乎没有差异；（ii）尽管存在少量的LHCA5，但通过用抗FLAG M2亲和凝胶孵育后提取样品，可以获得包含LHCA5的PSI-LHCI超级复合体，通过免疫印迹分析发现其中LHCA5替代了LHCA4；（iii）在PSI-LHCI超级复合体中用LHCA5替代LHCA4会导致低温荧光发射出现蓝移，表明远红光吸收减少。这些结果为理解LHCA4和LHCA5在绿色植物从水生到陆生生活方式进化过程中的位置和功能提供了新线索。
