Plant and Cell Physiology最新文献

The initiation of starch granule synthesis remains a relatively poorly understood phenomenon. Recent advances enabled the establishment of a model explaining the synthesis of new starch granules in Arabidopsis thaliana. These characterizations revealed the involvement of both a specific starch synthase isoform (SS4) and of several non-enzymatic proteins in this process. In this work, we investigated whether the initiation of starch synthesis in the green microalgae Chlamydomonas reinhardtii involves the same machinery as those uncovered in the plant model. Our extensive phylogenetic analysis revealed that most of the key players that were identified in higher plants are not found in microalgae suggesting that a different pathway is taking place. We showed that restoration of ADP-glucose synthesis in a mutant strain devoid of any endogenous primers allowed normal starch synthesis, revealing the existence of an initiation mechanism in Chlamydomonas. Our biochemical characterizations revealed that starch synthase isoform 3 possesses the intrinsic capacity to initiate polysaccharide synthesis in vitro and could be one of the functions involved in starch initiation. Our work suggests that the initiation of starch synthesis in Chlamydomonas involves a different pathway to that described in Arabidopsis and that further efforts will be required to identify the proteins involved in this process.

Cold stress is a major factor limiting rice (Oryza sativa L.) productivity, making it crucial to understand the molecular mechanisms underlying stress responses to develop resilient crops. In this study, we characterized OsZOS2-19, a cold- and abscisic acid (ABA) -responsive C2H2 zinc finger protein, which functions as a transcriptional repressor. Overexpression of OsZOS2-19 in rice lines increases sensitivity both cold and ABA, reducing cold tolerance, disrupting osmotic balance, and impairing reactive oxygen species (ROS) scavenging. RNA sequencing revealed that OsZOS2-19 overexpression interfered with key stress-response pathways, including those associated with sugar metabolism and glutathione biosynthesis. These findings suggest that OsZOS2-19 negatively regulates cold tolerance and ABA sensitivity by modulating ROS accumulation and osmotic balance, offering new insights into cold adaptation in rice.

Epigenetic modifications in plants involve heritable changes in gene expression patterns that are not due to changes in gene sequences. Unlike genetic adaptations, which are long-term evolutionary changes, epigenetic modifications, such as DNA methylation, histone modifications, and non-coding RNAs, act as adaptive responses and allow plants to better cope with environmental stresses. As mangroves are uniquely located between the land and sea and remain continuously exposed to varying salinity, submergence, and hypoxia stresses, it is expected that certain epigenetic mechanisms might help them withstand the impacts of recurring stress fluctuations. Therefore, understanding the role of epigenetic regulation in mangrove stress adaptations to the intertidal environment is crucial. Despite only few studies to date having investigated epigenetic responses in mangroves, they nonetheless provide important insights into this process on which to base future research. Here, we present an update on recent progress in mangrove epigenetic research and offer perspectives on the potential roles of various epigenetic players in mangrove adaptations to the intertidal environment.

Plant genetic variation can play a key role in shaping ecological communities. Prior work investigated the effects of coarse-grain variation among plant genotypes on their diverse arthropod communities. Several recent studies, however, have leveraged the boom of genomic resources to study how genome-wide plant variation influences associated communities. These studies have demonstrated that the effects of plant genomic variation are not just detectable but can be important drivers of arthropod communities in natural ecosystems. Field common gardens and lab-based mesocosm experiments are also revealing candidate genes that have large effects on arthropod communities. While we highlight these exciting results, we also discuss key challenges to address in future research. We argue that a major hurdle lies in the integration of genomic tools with hierarchical models of species communities (HMSC). HMSC are generative models that provide the opportunity to not only better understand the processes underlying community change, but to also predict community dynamics. We also advocate for future research to apply models of genomic prediction to explore the genetic architecture of arthropod community phenotypes. We hypothesize that this genetic architecture will follow an exponential distribution, where a few genes of large effect, but also many genes of small effect, contribute to variation in arthropod communities. The next generation of studies linking plant genes to community dynamics will require interdisciplinary collaborations to build truly predictive models of plant genetic and arthropod community change.

Plants control their stomatal apertures to optimize carbon dioxide uptake and water loss. Stomata open in response to light through the phosphorylation of the penultimate residue, Thr, of plasma membrane (PM) H+-ATPase in guard cells. Stomata close in response to drought and the phytohormone abscisic acid (ABA), and ABA suppresses the light-induced activation of PM H+-ATPase. However, the signaling pathways that regulate the stomatal aperture remain unclear. Previously, we identified a target of rapamycin (TOR) inhibitor, temsirolimus, to induce stomatal opening through chemical screening. In the present study, we further investigated other TOR inhibitors and identified PP242 as a novel stomatal opening chemical. PP242 induced stomatal opening even in the dark, as well as phosphorylation of the penultimate Thr of PM H+-ATPase in guard cells. Interestingly, PP242 completely suppressed ABA-induced stomatal closure, and inhibited ABA-induced activation of SNF1-related protein kinase 2s (SnRK2s), which are essential kinases for ABA signal transduction in guard cells. In vitro biochemical analysis revealed that PP242 did not directly inhibit SnRK2 but rather inhibited upstream ABA signaling components, specifically B3 clade Raf-like kinases. A quadruple mutant of B3 clade Raf-like kinases exhibited an open stoma phenotype that resembled the effect of PP242. However, PP242 still induced stomatal opening in this mutant, suggesting that PP242 also targets other guard cell components. Together, these results reveal that PP242 induces stomatal opening partly by inhibiting steady-state ABA signal transduction.

Reverse transcription quantitative real-time PCR (RT-qPCR) is esteemed for its precision and reliability, positioning it as the standard for evaluating gene expression. Selecting suitable reference genes is crucial for acquiring accurate data on target gene expression. However, identifying appropriate reference genes for specific rice tissues or growth conditions has been a challenge. To overcome this, we introduce the Rice Reference Genes (RRG) tool ( https://www.rrgenes.com/ ), which assists researchers in selecting reference genes for diverse experimental conditions in rice. This tool utilizes 4404 rice-derived RNA-seq datasets, categorized by five tissue types-leaf, root, seedling, panicle, and seed-and seven stress conditions (cold, disease, drought, heat, hormone, metal, and salt), along with corresponding control groups (mock). In this research, we employed the RRG web-based tool to identify candidate reference genes in rice leaves, roots, and seedlings exposed to salt and drought stress. These candidates were rigorously tested against conventionally established reference genes, confirming their accuracy and reliability. The RRG tool is designed to be user-friendly, allowing even those with limited experience to efficiently select optimal reference genes in rice with ease.

Plants exhibit shoot growth in the direction of the light source to facilitate photosynthesis, known as positive phototropism. In Arabidopsis hypocotyl phototropism, it is thought that a gradient of the signal intensity of the blue light (BL) photoreceptor phototropin1 (phot1) between the light-irradiated and shaded sides leads to the differential growth of hypocotyls. The intensity of phot1 signal is regulated not only by the protein kinase activity of phot1 but also by the phosphorylation status of the NONPHOTOTROPIC HYPOCOTYL3 (NPH3) protein, which has a dark form and a BL form of the phosphorylation modification. Previous studies have shown that phot1 drives the forward reaction from the dark form to the BL form of NPH3. However, the molecular mechanism underlying the reverse reaction remains unknown. Here, we show that protein phosphatase PP2C19 controls the reverse reaction that converts the BL form of NPH3 to the dark form of NPH3. The PP2C19 protein possesses the protein phosphatase type 2C (PP2C) domain, two cyclic nucleoside monophosphate (cNMP)-binding domains, and the protein kinase domain. Similar to phot1 and NPH3, PP2C19 localizes to the plasma membrane, and its PP2C domain is necessary and sufficient for PP2C19 function in hypocotyl phototropism. The pp2c19 mutants show abnormalities in second positive hypocotyl phototropism with a delay in the reverse reaction of NPH3 phosphorylation modification. The present study suggests that continuous BL irradiation induces an equilibrium state of the reversible reaction of NPH3 phosphorylation, which acts as a phot1 signaling gradient with phot1 kinase activity to induce the second positive phototropism.

Recently, acyl plastoquinol (APQ) and plastoquinone-B (PQ-B), which are fatty acid esters of plastoquinol and plastoquinone-C respectively, have been identified as the major neutral lipids in cyanobacteria. In Synechocystis sp. PCC 6803, Slr2103 having homology with the eukaryotic enzyme for triacylglycerol (TAG) synthesis, diacylglycerol acyltransferase 2 (DGAT2), was identified as responsible for the synthesis of these plastoquinone-related lipids. On the other hand, TAG synthesis in cyanobacteria remains controversial due to the low accumulation level within cyanobacterial cells together with the high contamination level from the environment. In this study, to quantify more precisely and elucidate the relationship between the accumulation of neutral lipids and the presence or absence of DGAT2-like genes, plastoquinone-related lipids and TAG were analyzed directly from total lipids of six cyanobacterial species with different sets of genes encoding DGAT2-like proteins belonging to two distinct subclades. The results showed that the synthesis of these neutral lipids is highly dependent on clade A DGAT2-like proteins under the culture conditions used in this study, although accumulation level of TAG was quite low. In contrast to APQ highly abundant in saturated fatty acids, the fatty acid composition of TAG was species-specific and partly reflected the total lipid composition. Gloeobacter violaceus PCC 7421, which lacks a DGAT2-like gene, accumulated APQ with a high proportion of C18:0, suggesting APQ synthesis by an unidentified acyltransferase.

Diversification of the cellulose synthase superfamily of glycosyltransferases has provided plants with the ability to synthesize varied cell wall polysaccharides such as xyloglucan, mannans, and the mixed-linkage glucans of cereals. Surprisingly, some but not all members of the cellulose synthase-like M (CslM) gene family have recently been shown to be involved in the glycosylation of the aglycone core of a range of triterpenoid saponins. However, no cell wall activity has yet been attributed to any of the CslM gene family members. Here, evolution of the CslM gene family in eudicots is explored to better understand the differences between the two metabolically distinct classes of CslMs (CslM1 and CslM2) and the very closely related CslGs. To achieve this, a robust tBLASTn approach was developed to identify CslM1, CslM2, and CslG sequences using diagnostic peptides, suitable for complex genomes using unannotated and short-read datasets. To ascertain whether both CslM1 and CslM2 proteins have cell wall functions, in addition to the 'saponin' role of CslM2, tomato CslM1 and CslM2 genes were ectopically expressed in Arabidopsis thaliana by stable transformation and in the transient Nicotiana benthamiana system. Transformed plants were analysed with immunofluorescence, immunogold transmission electron microscopy, and cell wall polysaccharides were extracted for monosaccharide linkage analysis. Our results support a role for both CslM1 and CslM2 in the biosynthesis of type II arabinogalactan linkages, generating new insight into how the diverse functions of CslMs can coexist and providing clear targets for future research.

The emergence of unisexual flower is an important event during plant evolution. The molecular mechanism underlying the formation of unisexual flowers remains unclear in dioecious spinach. In this study, we identified the spinach MALE STERILITY1 gene, SpMS1, which serves as a masculine factor to regulate male fertility and sex reversion. Silencing SpMS1 led to stamen sterility in male flowers and the development of masculine traits in female flowers. Overexpression of SpMS1 in wild-type Arabidopsis resulted in sterile stamens and irregular pollen exine. Notably, ectopic expression of SpMS1 in Arabidopsis ms1 mutants restored pollen viability and flower fertility. Furthermore, our findings demonstrate that SpMS1 interacts with MADS-box transcription factor SpAP1 to regulate unisexual flower development. Thus, SpMS1 exhibits a conserved function in pollen fertility akin to bisexual flowers, while also acting as a key regulator of unisexual flower development in spinach. This study sheds light on the mechanism of sex differentiation in dioecious plants and also provides valuable insights for manipulating male sterility in plant breeding programs.