Devadasu Elsinraju, Kanna Sai Divya, Neelam Satyabala, Yadav Ranay Mohan, Nama Srilatha, Akhtar Parveen, Polgár Tamás F, Ughy Bettina, Garab Győző, Lambrev Petar H, Subramanyam Rajagopal
Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad, India.
Institute of Plant Biology, Biological Research Centre, Eötvös Loránd Research Network, Szeged, Hungary.
Front Plant Sci. 2023 Apr 5;14:1051711. doi: 10.3389/fpls.2023.1051711. eCollection 2023.
Salt stress triggers an Stt7-mediated LHCII-phosphorylation signaling mechanism similar to light-induced state transitions. However, phosphorylated LHCII, after detaching from PSII, does not attach to PSI but self-aggregates instead. Salt is a major stress factor in the growth of algae and plants. Here, our study mainly focuses on the organization of the photosynthetic apparatus to the long-term responses of to elevated NaCl concentrations. We analyzed the physiological effects of salt treatment at a cellular, membrane, and protein level by microscopy, protein profile analyses, transcripts, circular dichroism spectroscopy, chlorophyll fluorescence transients, and steady-state and time-resolved fluorescence spectroscopy. We have ascertained that cells that were grown in high-salinity medium form palmelloids sphere-shaped colonies, where daughter cells with curtailed flagella are enclosed within the mother cell walls. Palmelloid formation depends on the presence of a cell wall, as it was not observed in a cell-wall-less mutant CC-503. Using the mutant cells, we show Stt7 kinase-dependent phosphorylation of light-harvesting complex II (LHCII) in both short- and long-term treatments of various NaCl concentrations-demonstrating NaCl-induced state transitions that are similar to light-induced state transitions. The grana thylakoids were less appressed (with higher repeat distances), and cells grown in 150 mM NaCl showed disordered structures that formed diffuse boundaries with the flanking stroma lamellae. PSII core proteins were more prone to damage than PSI. At high salt concentrations (100-150 mM), LHCII aggregates accumulated in the thylakoid membranes. Low-temperature and time-resolved fluorescence spectroscopy indicated that the mutant was more sensitive to salt stress, suggesting that LHCII phosphorylation has a role in the acclimation and protection of the photosynthetic apparatus.
盐胁迫触发了一种类似于光诱导状态转换的由Stt7介导的LHCII磷酸化信号传导机制。然而，从PSII脱离后的磷酸化LHCII并不附着于PSI，而是发生自我聚集。盐是藻类和植物生长中的主要胁迫因素。在此，我们的研究主要聚焦于光合机构对升高的NaCl浓度的长期响应的组织情况。我们通过显微镜检查、蛋白质谱分析、转录本、圆二色光谱、叶绿素荧光瞬变以及稳态和时间分辨荧光光谱，在细胞、膜和蛋白质水平分析了盐处理的生理效应。我们已经确定，在高盐培养基中生长的细胞形成了似球藻球形菌落，其中带有缩短鞭毛的子细胞被包裹在母细胞壁内。似球藻的形成取决于细胞壁的存在，因为在无细胞壁突变体CC - 503中未观察到这种现象。利用突变细胞，我们发现在不同NaCl浓度的短期和长期处理中，光捕获复合物II（LHCII）存在Stt7激酶依赖性磷酸化，这表明NaCl诱导的状态转换类似于光诱导的状态转换。基粒类囊体的堆积程度较低（重复距离更大），在150 mM NaCl中生长的细胞显示出无序结构，与侧翼的基质类囊体形成弥散边界。PSII核心蛋白比PSI更容易受到损伤。在高盐浓度（100 - 150 mM）下，LHCII聚集体在类囊体膜中积累。低温和时间分辨荧光光谱表明突变体对盐胁迫更敏感，这表明LHCII磷酸化在光合机构的适应和保护中发挥作用。
