Plant Cell最新文献

In oxygenic photosynthesis, state transitions distribute light energy between PSI and PSII. This regulation involves reduction of the plastoquinone pool, activation of the state transitions 7 (STT7) protein kinase by the cytochrome (cyt) b6f complex, and phosphorylation and migration of light harvesting complexes II (LHCII). In this study, we show that in Chlamydomonas reinhardtii, the C-terminus of the cyt b6 subunit PetB acts on phosphorylation of STT7 and state transitions. We used site-directed mutagenesis of the chloroplast petB gene to truncate (remove L215b6) or elongate (add G216b6) the cyt b6 subunit. Modified complexes are devoid of heme ci and degraded by FTSH protease, revealing that salt bridge formation between cyt b6 (PetB) and Subunit IV (PetD) is essential to the assembly of the complex. In double mutants where FTSH is inactivated, modified cyt b6f accumulated but the phosphorylation cascade was blocked. We also replaced the arginine interacting with heme ci propionate (R207Kb6). In this modified complex, heme ci is present but the kinetics of phosphorylation are slower. We show that highly phosphorylated forms of STT7 accumulated transiently after reduction of the PQ pool and represent the active forms of the protein kinase. The phosphorylation of the LHCII targets is favored at the expense of the protein kinase, and the migration of LHCII toward PSI is the limiting step for state transitions.

Meiotic recombination is a key biological process in plant evolution and breeding, as it generates genetic diversity in each generation through the formation of crossovers (COs). However, due to their importance in genome stability, COs are highly regulated in frequency and distribution. We previously demonstrated that this strict regulation of COs can be modified, both in terms of CO frequency and distribution, in allotriploid Brassica hybrids (2n = 3x = 29; AAC) resulting from a cross between Brassica napus (2n = 4x = 38; AACC) and Brassica rapa (2n = 2x = 20; AA). Using the recently updated B. napus genome now including pericentromeres, we demonstrated that COs occur in these cold regions in allotriploids, as close as 375 kb from the centromere. Reverse transcription quantitative PCR (RT-qPCR) of various meiotic genes indicated that Class I COs are likely involved in the increased recombination frequency observed in allotriploids. We also demonstrated that this modified recombination landscape can be maintained via successive generations of allotriploidy (odd ploidy level). This deregulated meiotic behavior reverts to strict regulation in allotetraploid (even ploidy level) progeny in the second generation. Overall, we provide an easy way to manipulate tight recombination control in a polyploid crop.

During the floral transition, many plant species including chrysanthemum (Chrysanthemum morifolium) require continuous photoperiodic stimulation for successful anthesis. Insufficient photoperiodic stimulation results in flower bud arrest or even failure. The molecular mechanisms underlying how continuous photoperiodic stimulation promotes anthesis are not well understood. Here, we reveal that in wild chrysanthemum (Chrysanthemum indicum), an obligate short-day (SD) plant, floral evocation is not limited to SD conditions. However, SD signals generated locally in the inflorescence meristem (IM) play a vital role in ensuring anthesis after floral commitment. Genetic analyses indicate that the florigen FLOWERING LOCUS T-LIKE3 (CiFTL3) plays an important role in floral evocation, but a lesser role in anthesis. Importantly, our data demonstrate that AGAMOUS-LIKE 24 (CiAGL24) is a critical component of SD signal perception in the IM to promote successful anthesis, and that floral evocation and anthesis are two separate developmental events in chrysanthemum. We further reveal that the central circadian clock component PSEUDO-RESPONSE REGULATOR 7 (CiPRR7) in the IM activates CiAGL24 expression in response to SD conditions. Moreover, our findings elucidate a negative feedback loop in which CiAGL24 and SUPPRESSOR OF OVEREXPRESSION OF CO 1 (CiSOC1) modulate LEAFY (CiLFY) expression. Together, our results demonstrate that the CiPRR7-CiAGL24 module is vital for sustained SD signal perception in the IM to ensure successful anthesis in chrysanthemum.

The photosynthetic apparatus is formed by thylakoid membrane-embedded multiprotein complexes that carry out linear electron transport in oxygenic photosynthesis. The machinery is largely conserved from cyanobacteria to land plants, and structure and function of the protein complexes involved are relatively well studied. By contrast, how the machinery is assembled in thylakoid membranes remains poorly understood. The complexes participating in photosynthetic electron transfer are composed of many proteins, pigments, and redox-active cofactors, whose temporally and spatially highly coordinated incorporation is essential to build functional mature complexes. Several proteins, jointly referred to as assembly factors, engage in the biogenesis of these complexes to bring the components together in a step-wise manner, in the right order and time. In this review, we focus on the biogenesis of the terminal protein supercomplex of the photosynthetic electron transport chain, PSI, in vascular plants. We summarize our current knowledge of the assembly process and the factors involved and describe the challenges associated with resolving the assembly pathway in molecular detail.

Plants respond to cold stress at multiple levels, including increasing cytosolic calcium (Ca2+) influx and triggering the expression of cold-responsive genes. In this study, we show that the Ca2+-permeable channel CYCLIC NUCLEOTIDE-GATED CHANNEL20 (CNGC20) positively regulates freezing tolerance in Arabidopsis (Arabidopsis thaliana) by mediating cold-induced Ca2+ influx. Moreover, we demonstrate that the leucine-rich repeat receptor-like kinase PLANT PEPTIDE CONTAINING SULFATED TYROSINE1 RECEPTOR (PSY1R) is activated by cold, phosphorylating and enhancing the activity of CNGC20. The psy1r mutant exhibits decreased cold-evoked Ca2+ influx and freezing tolerance. Conversely, COLD-RESPONSIVE PROTEIN KINASE1 (CRPK1), a protein kinase that negatively regulates cold signaling, phosphorylates and facilitates the degradation of CNGC20 under prolonged periods of cold treatment, thereby attenuating freezing tolerance. This study thus identifies PSY1R and CRPK1 kinases that regulate CNGC20 activity and stability, respectively, thereby antagonistically modulating freezing tolerance in plants.

PROTON GRADIENT REGULATION5 (PGR5) is thought to promote cyclic electron flow, and its deficiency impairs photosynthetic control and increases photosensitivity of photosystem (PS) I, leading to seedling lethality under fluctuating light (FL). By screening for Arabidopsis (Arabidopsis thaliana) suppressor mutations that rescue the seedling lethality of pgr5 plants under FL, we identified a portfolio of mutations in 12 different genes. These mutations affect either PSII function, cytochrome b6f (cyt b6f) assembly, plastocyanin (PC) accumulation, the CHLOROPLAST FRUCTOSE-1,6-BISPHOSPHATASE1 (cFBP1), or its negative regulator ATYPICAL CYS HIS-RICH THIOREDOXIN2 (ACHT2). The characterization of the mutants indicates that the recovery of viability can in most cases be explained by the restoration of PSI donor side limitation, which is caused by reduced electron flow to PSI due to defects in PSII, cyt b6f, or PC. Inactivation of cFBP1 or its negative regulator ACHT2 results in increased levels of the NADH dehydrogenase-like complex. This increased activity may be responsible for suppressing the pgr5 phenotype under FL conditions. Plants that lack both PGR5 and DE-ETIOLATION-INDUCED PROTEIN1 (DEIP1)/NEW TINY ALBINO1 (NTA1), previously thought to be essential for cyt b6f assembly, are viable and accumulate cyt b6f. We suggest that PGR5 can have a negative effect on the cyt b6f complex and that DEIP1/NTA1 can ameliorate this negative effect.

Microalgae contribute to about half of global net photosynthesis, which converts sunlight into the chemical energy (ATP and NADPH) used to transform CO2 into biomass. Alternative electron pathways of photosynthesis have been proposed to generate additional ATP that is required to sustain CO2 fixation. However, the relative importance of each alternative pathway remains elusive. Here, we dissect and quantify the contribution of cyclic, pseudo-cyclic, and chloroplast-to-mitochondrion electron flows for their ability to sustain net photosynthesis in the microalga Chlamydomonas reinhardtii. We show that (i) each alternative pathway can provide sufficient additional energy to sustain high CO2 fixation rates, (ii) the alternative pathways exhibit cross-compensation, and (iii) the activity of at least one of the three alternative pathways is necessary to sustain photosynthesis. We further show that all pathways have very different efficiencies at energizing CO2 fixation, with the chloroplast-mitochondrion interaction being the most efficient. Overall, our data lay bioenergetic foundations for biotechnological strategies to improve CO2 capture and fixation.

As an essential intrinsic component of photosystem II (PSII) in all oxygenic photosynthetic organisms, heme-bridged heterodimer cytochrome b559 (Cyt b559) plays critical roles in the protection and assembly of PSII. However, the underlying mechanisms of Cyt b559 assembly are largely unclear. Here, we characterized the Arabidopsis (Arabidopsis thaliana) rph1 (resistance to Phytophthora1) mutant, which was previously shown to be susceptible to the oomycete pathogen Phytophthora brassicae. Loss of RPH1 leads to a drastic reduction in PSII accumulation, which can be primarily attributed to the defective formation of Cyt b559. Spectroscopic analyses showed that the heme level in PSII supercomplexes isolated from rph1 is significantly reduced, suggesting that RPH1 facilitates proper heme assembly in Cyt b559. Due to the loss of RPH1-mediated processes, a covalently bound PsbE-PsbF heterodimer is formed during the biogenesis of PSII. In addition, rph1 is highly photosensitive and accumulates elevated levels of reactive oxygen species under photoinhibitory-light conditions. RPH1 is a conserved intrinsic thylakoid protein present in green algae and terrestrial plants, but absent in Synechocystis, and it directly interacts with the subunits of Cyt b559. Thus, our data demonstrate that RPH1 represents a chloroplast acquisition specifically promoting the efficient assembly of Cyt b559, probably by mediating proper heme insertion into the apo-Cyt b559 during the initial phase of PSII biogenesis.

Alternative splicing (AS) plays crucial roles in regulating various biological processes in plants. However, the genetic mechanisms underlying AS and its role in controlling important agronomic traits in rice (Oryza sativa) remain poorly understood. In this study, we explored AS in rice leaves and panicles using the rice minicore collection. Our analysis revealed a high level of transcript isoform diversity, with approximately one-fifth of the potential isoforms acting as major transcripts in both tissues. Regarding the genetic mechanism of AS, we found that the splicing of 833 genes in the leaf and 1,230 genes in the panicle was affected by cis-genetic variation. Twenty-one percent of these AS events could only be explained by large structural variations. Approximately 77.5% of genes with significant splicing quantitative trait loci (sGenes) exhibited tissue-specific regulation, and AS can cause 26.9% (leaf) and 23.6% (panicle) of sGenes to have altered, lost, or gained functional domains. Additionally, through splicing-phenotype association analysis, we identified phosphate-starvation-induced RING-type E3 ligase (OsPIE1; LOC_Os01g72480), whose splicing ratio was significantly associated with plant height. In summary, this study provides an understanding of AS in rice and its contribution to the regulation of important agronomic traits.