Applied Science and Technology Department-BioSolar Lab, Politecnico di Torino, 10144, Torino, Italy.
ISALIT-Department of Science and Technological Innovation, University of Eastern Piedmont, 15121, Alessandria, Italy.
Physiol Plant. 2019 May;166(1):336-350. doi: 10.1111/ppl.12964.
About 475 million years ago, plants originated from an ancestral green alga and evolved first as non-vascular and later as vascular plants, becoming the primary producers of biomass on lands. During that time, the light-harvesting complex II (LHCII), responsible for sunlight absorption and excitation energy transfer to the photosystem II (PSII) core, underwent extensive differentiation. Lhcb4 is an ancestral LHCII that, in flowering plants, differentiated into up to three isoforms, Lhcb4.1, Lhcb4.2 and Lhcb4.3. The pivotal position of Lhcb4 in the PSII-LHCII supercomplex (PSII-LHCIIsc) allows functioning as linker for either S- or M-trimers of LHCII to the PSII core. The increased accumulation of Lhcb4.3 observed in PSII-LHCIIsc of plants acclimated to moderate and high light intensities induced us to investigate, whether this isoform has a preferential localization in a specific PSII-LHCIIsc conformation that might explain its light-dependent accumulation. In this work, by combining an improved method for separation of different forms of PSII-LHCIIsc from thylakoids of Pisum sativum L. grown at increasing irradiances with quantitative proteomics, we assessed that Lhcb4.3 is abundant in PSII-LHCIIsc of type C S , and, interestingly, similar results were found for the PsbR subunit. Phylogenetic comparative analysis on different taxa of the Viridiplantae lineage and structural modeling further pointed out to an effect of the evolution of different Lhcb4 isoforms on the light-dependent modulation of the PSII-LHCIIsc organization. This information provides new insight on the properties of the Lhcb4 and its isoforms and their role on the structure, function and regulation of PSII.
大约 4.75 亿年前，植物起源于一个祖先绿藻，并首先进化为非维管束植物，然后进化为维管束植物，成为陆地上生物量的主要生产者。在此期间，负责吸收阳光和将激发能转移到光系统 II (PSII) 核心的光捕获复合物 II (LHCII) 经历了广泛的分化。Lhcb4 是一种祖先 LHCII，在开花植物中，它分化为多达三种同工型，Lhcb4.1、Lhcb4.2 和 Lhcb4.3。Lhcb4 在 PSII-LHCII 超复合物 (PSII-LHCIIsc) 中的关键位置允许它作为 LHCII 的 S-或 M-三聚体与 PSII 核心的连接体发挥作用。在适应中强和高光强的植物的 PSII-LHCIIsc 中观察到 Lhcb4.3 的积累增加，这促使我们研究这种同工型是否优先定位于特定的 PSII-LHCIIsc 构象，这可能解释其光依赖性积累。在这项工作中，我们结合了一种从豌豆叶片中分离不同形式 PSII-LHCIIsc 的改良方法，这种方法是在不断增加的辐照度下生长的，并用定量蛋白质组学对其进行了评估，结果表明 Lhcb4.3 在 PSII-LHCIIsc 的 C 型 S 中含量丰富，有趣的是，PsbR 亚基也有类似的结果。对不同类群的绿藻植物的系统发育比较分析和结构建模进一步指出，不同 Lhcb4 同工型的进化对 PSII-LHCIIsc 组织的光依赖性调节有影响。这些信息为 Lhcb4 及其同工型的特性及其在 PSII 结构、功能和调节中的作用提供了新的见解。
