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    A unique photosystem I reaction center from a chlorophyll d-containing cyanobacterium Acaryochloris marina
    Caihuang Xu, Qingjun Zhu, Jing‐Hua Chen, Liangliang Shen, Xiaohan Yi, Zihui Huang, Wenda Wang, Min Chen, Tingyun Kuang, Jian‐Ren Shen, Xing Zhang and Guangye Han
    J Integr Plant Biol 2021, 63 (10): 1740-1752.  
    doi: 10.1111/jipb.13113
    Abstract (Browse 185)  |   Save
    Photosystem I (PSI) is a large protein supercomplex that catalyzes the light-dependent oxidation of plastocyanin (or cytochrome c6) and the reduction of ferredoxin. This catalytic reaction is realized by a transmembrane electron transfer chain consisting of primary electron donor (a special chlorophyll (Chl) pair) and electron acceptors A0, A1, and three Fe4S4 clusters, FX, FA, and FB. Here we report the PSI structure from a Chl d-dominated cyanobacterium Acaryochloris marina at 3.3 Å resolution obtained by single-particle cryo-electron microscopy. The A. marina PSI exists as a trimer with three identical monomers. Surprisingly, the structure reveals a unique composition of electron transfer chain in which the primary electron acceptor A0 is composed of two pheophytin a rather than Chl a found in any other well-known PSI structures. A novel subunit Psa27 is observed in the A. marina PSI structure. In addition, 77 Chls, 13 α-carotenes, two phylloquinones, three Fe-S clusters, two phosphatidyl glycerols, and one monogalactosyl-diglyceride were identified in each PSI monomer. Our results provide a structural basis for deciphering the mechanism of photosynthesis in a PSI complex with Chl d as the dominating pigments and absorbing far-red light.
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    From genes to networks: The genetic control of leaf development
    Hongfeng Wang, Fanjiang Kong and Chuanen Zhou
    J Integr Plant Biol 2021, 63 (7): 1181-1196.  
    doi: 10.1111/jipb.13084
    Abstract (Browse 361)  |   Save
    Substantial diversity exists for both the size and shape of the leaf, the main photosynthetic organ of flowering plants. The two major forms of leaf are simple leaves, in which the leaf blade is undivided, and compound leaves, which comprise several leaflets. Leaves form at the shoot apical meristem from a group of undifferentiated cells, which first establish polarity, then grow and differentiate. Each of these processes is controlled by a combination of transcriptional regulators, microRNAs and phytohormones. The present review documents recent advances in our understanding of how these various factors modulate the development of both simple leaves (focusing mainly on the model plant Arabidopsis thaliana) and compound leaves (focusing mainly on the model legume species Medicago truncatula).
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    Structure of plant photosystem I−light harvesting complex I supercomplex at 2.4 Å resolution
    Jie Wang, Long‐Jiang Yu, Wenda Wang, Qiujing Yan, Tingyun Kuang, Xiaochun Qin and Jian‐Ren Shen
    J Integr Plant Biol 2021, 63 (7): 1367-1381.  
    DOI: 10.1111/jipb.13095
    Abstract (Browse 215)  |   Save
    Photosystem I (PSI) is one of the two photosystems in photosynthesis, and performs a series of electron transfer reactions leading to the reduction of ferredoxin. In higher plants, PSI is surrounded by four light-harvesting complex I (LHCI) subunits, which harvest and transfer energy efficiently to the PSI core. The crystal structure of PSI-LHCI supercomplex has been analyzed up to 2.6 Å resolution, providing much information on the arrangement of proteins and cofactors in this complicated supercomplex. Here we have optimized crystallization conditions, and analyzed the crystal structure of PSI-LHCI at 2.4 Å resolution. Our structure showed some shift of the LHCI, especially the Lhca4 subunit, away from the PSI core, suggesting the indirect connection and inefficiency of energy transfer from this Lhca subunit to the PSI core. We identified five new lipids in the structure, most of them are located in the gap region between the Lhca subunits and the PSI core. These lipid molecules may play important roles in binding of the Lhca subunits to the core, as well as in the assembly of the supercomplex. The present results thus provide novel information for the elucidation of the mechanisms for the light-energy harvesting, transfer and assembly of this supercomplex.
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    Light participates in the auxin‐dependent regulation of plant growth
    Bingsheng Lv, Jiayong Zhu, Xiangpei Kong and Zhaojun Ding
    J Integr Plant Biol 2021, 63 (5): 819-822.  
    doi: 10.1111/jipb.13036
    Abstract (Browse 335)  |   Save
    Light is the energy source for plant photosynthesis and influences plant growth and development. Through multiple photoreceptors, plant interprets light signals through various downstream phytohormones such as auxin. Recently, Chen et al. (2020) uncover a new layer of regulation in IPyA pathway of auxin biosynthesis by light. Here we highlight recent studies about how light controls plant growth through regulating auxin biosynthesis and signaling.
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    Pentatricopeptide repeat protein PHOTOSYSTEM I BIOGENESIS FACTOR2 is required for splicing of ycf3
    Xuemei Wang, Zhipan Yang, Yi Zhang, Wen Zhou, Aihong Zhang and Congming Lu
    J Integr Plant Biol 2020, 62 (11): 1741-1761.  
    DOI: 10.1111/jipb.12936
    Abstract (Browse 285)  |   Save

    To gain a better understanding of the molecular mechanisms of photosystem I (PSI) biogenesis, we characterized the Arabidopsis thaliana photosystem I biogenesis factor 2 (pbf2) mutant, which lacks PSI complex. PBF2 encodes a P‐class pentatricopeptide repeat (PPR) protein. In the pbf2 mutants, we observed a striking decrease in the transcript level of only one gene, the chloroplast gene ycf3, which is essential for PSI assembly. Further analysis of ycf3 transcripts showed that PBF2 is specifically required for the splicing of ycf3 intron 1. Computational prediction of binding sequences and electrophoretic mobility shift assays reveal that PBF2 specifically binds to a sequence in ycf3 intron 1. Moreover, we found that PBF2 interacted with two general factors for group II intron splicing CHLOROPLAST RNA SPLICING2‐ASSOCIATED FACTOR1 (CAF1) and CAF2, and facilitated the association of these two factors with ycf3 intron 1. Our results suggest that PBF2 is specifically required for the splicing of ycf3 intron 1 through cooperating with CAF1 and CAF2. Our results also suggest that additional proteins are required to contribute to the specificity of CAF‐dependent group II intron splicing.

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    Plastid ribosomal protein LPE2 is involved in photosynthesis and the response to C/N balance in Arabidopsis thaliana
    Xiaoxiao Dong, Sujuan Duan, Hong-Bin Wang and Hong-Lei Jin
    J Integr Plant Biol 2020, 62 (9): 1418-1432.  
    doi: 10.1111/jipb.12907
    Abstract (Browse 373)  |   Save

    The balance between cellular carbon (C) and nitrogen (N) must be tightly coordinated to sustain optimal growth and development in plants. In chloroplasts, photosynthesis converts inorganic C to organic C, which is important for maintenance of C content in plant cells. However, little is known about the role of chloroplasts in C/N balance. Here, we identified a nuclear‐encoded protein LOW PHOTOSYNTHETIC EFFICIENCY2 (LPE2) that it is required for photosynthesis and C/N balance in Arabidopsis. LPE2 is specifically localized in the chloroplast. Both loss‐of‐function mutants, lpe2‐1 and lpe2‐2, showed lower photosynthetic activity, characterized by slower electron transport and lower PSII quantum yield than the wild type. Notably, LPE2 is predicted to encode the plastid ribosomal protein S21 (RPS21). Deficiency of LPE2 significantly perturbed the thylakoid membrane composition and plastid protein accumulation, although the transcription of plastid genes is not affected obviously. More interestingly, transcriptome analysis indicated that the loss of LPE2 altered the expression of C and N response related genes in nucleus, which is confirmed by quantitative real‐time‐polymerase chain reaction. Moreover, deficiency of LPE2 suppressed the response of C/N balance in physiological level. Taken together, our findings suggest that LPE2 plays dual roles in photosynthesis and the response to C/N balance.

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    Arabidopsis DXO1 possesses deNADding and exonuclease activities and its mutation affects defense-related and photosynthetic gene expression
    Shuying Pan, Kai-en Li, Wei Huang, Huan Zhong, Huihui Wu, Yuan Wang, He Zhang, Zongwei Cai, Hongwei Guo, Xuemei Chen and Yiji Xia
    J Integr Plant Biol 2020, 62 (7): 967-983.  
    doi: 10.1111/jipb.12867
    Abstract (Browse 421)  |   Save

    RNA capping and decapping tightly coordinate with transcription, translation, and RNA decay to regulate gene expression. Proteins in the DXO/Rai1 family have been implicated in mRNA decapping and decay, and mammalian DXO was recently found to also function as a decapping enzyme for NAD+‐capped RNAs (NAD‐RNA). The Arabidopsis genome contains a single gene encoding a DXO/Rai1 protein, AtDXO1. Here we show that AtDXO1 possesses both NAD‐RNA decapping activity and 5ʹ‐3ʹ exonuclease activity but does not hydrolyze the m7G cap. The atdxo1 mutation increased the stability of NAD‐RNAs and led to pleiotropic phenotypes, including severe growth retardation, pale color, and multiple developmental defects. Transcriptome profiling analysis showed that the atdxo1 mutation resulted in upregulation of defense‐related genes but downregulation of photosynthesis‐related genes. The autoimmunity phenotype of the mutant could be suppressed by either eds1 or npr1 mutation. However, the various phenotypes associated with the atdxo1 mutant could be complemented by an enzymatically inactive AtDXO1. The atdxo1 mutation apparently enhances post‐transcriptional gene silencing by elevating levels of siRNAs. Our study indicates that AtDXO1 regulates gene expression in various biological and physiological processes through its pleiotropic molecular functions in mediating RNA processing and decay.

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    The central circadian clock proteins CCA1 and LHY regulate iron homeostasis in Arabidopsis
    Gang Xu, Zhimin Jiang, Haiyang Wang and Rongcheng Lin
    J Integr Plant Biol 2019, 61 (2): 168-181.  
    DOI: 10.1111/jipb.12696
    Abstract (Browse 234)  |   Save
    Circadian clock is the endogenous time-keeping machinery that synchronizes an organism's metabolism, behavior, and physiology to the daily light-dark circles, thereby contributing to organismal fitness. Iron (Fe) is an essential micronutrient for all organisms and it plays important roles in diverse processes of plant growth and development. Here, we show that, in Arabidopsis thaliana, loss of the central clock genes, CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY), results in both reduced Fe uptake and photosynthetic efficiency, whereas CCA1 overexpression confers the opposite effects. We show that root Fe(III) reduction activity, and expression of FERRIC REDUCTION OXIDASE 2 (FRO2) and IRON-REGULATED TRANSPORTER 1 (IRT1) exhibit circadian oscillations, which are disrupted in the cca1 lhy double mutant. Furthermore, CCA1 directly binds to the specific regulatory regions of multiple Fe homeostasis genes and activates their expression. Thus, this study established that, in plants, CCA1 and LHY function as master regulators that maintain cyclic Fe homeostasis.
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