Plant and Cell Physiology最新文献

Artificial pentatricopeptide repeat (PPR) proteins (called as well designer PPR or dPPRs) are customized RNA binding proteins made of tandem repeats of a consensus 35 amino acid motif whose RNA base recognition can be programmed by the use of a two amino acid code. Recently, we designed an artificial PPR protein called dPPRrbcL based on a PPR consensus repeat scaffold flanked by N-terminal and C-terminal domains (NTD and CTD) derived from the native maize protein PPR10, and successfully expressed this protein in Arabidopsis chloroplasts to stabilize a processed 5'-end of rbcL mRNA. While the PPR repeats in dPPRs are expected to confer RNA binding and protection from exoribonuclease, the importance of the N-terminal and C-terminal domains for dPPR in vivo activity remains unknown. Here, we used functional complementation assays in Arabidopsis using truncated versions of dPPRrbcL to examine the contribution of the NTD and CTD to rbcL mRNA stabilization in chloroplasts. The results showed that the NTD and CTD are not required for the in vivo stabilization of the processed 5' end of rbcL mRNA by dPPRrbcL but the NTD likely protects a few nucleotides at the 5'-end of the RNA sequence bound by the PPR motifs against the action of exoribonucleases. These discoveries indicate that a PPR repeat scaffold itself is sufficient to efficiently stabilize processed RNAs in chloroplasts.

Target of rapamycin (TOR) signaling plays a pivotal role in regulating various cellular processes, including energy metabolism and growth. In this study, we investigated the impact of TOR inhibition on maize radicle development, focusing on energy homeostasis and starch metabolism. We found that TOR inhibition significantly decreased the ATP/AMP ratio, indicating a disruption in cellular energy balance. This was accompanied by alterations in the expression of genes related to energy metabolism, such as STP1 (SUGAR TRANSPORTER PROTEIN 1) and ASN1 (Aspartate Aminotransferase 1). Transcriptomic and metabolomic analyses revealed significant changes in carbohydrate metabolism, particularly in starch degradation pathways, with key metabolites like glucose-6-phosphate (G6P) showing marked reductions. To further elucidate the role of starch metabolism in TOR-mediated regulation of radicle growth, we performed rescue experiments using exogenous soluble starch and maltose. Both treatments alleviated the inhibitory effects of TOR suppression, with radicle length increasing by 19.7% and 37.0%, respectively. These results highlight that TOR signaling regulates radicle development by modulating starch metabolism and energy homeostasis. Our findings provide new insights into the molecular mechanisms underlying TOR-mediated growth regulation and suggest that manipulating starch metabolism could be a potential strategy to enhance seedling development under stress conditions.

Several plant species adapted to low-phosphorus (P) conditions develop cluster roots, specialized structures that release organic acids and acid phosphatases (APases) to increase inorganic phosphate (Pi) availability. White lupin (Lupinus albus L.) is used as a model for studying cluster root function. Using a positron-emitting tracer imaging system (PETIS), we previously observed spot-like carbon (C) secretion patterns in the cluster roots of white lupin, the amounts of which differed widely among spots, suggesting variation in secretion activity among cluster roots. Here, we combined PETIS with RNA-Seq to investigate transcriptomic differences between cluster roots with varying secretion activities. We identified 564 genes positively correlated and 135 genes negatively correlated with secretion levels. Among the positively correlated genes, we found three aluminum-activated malate transporter genes and two multidrug and toxic compound extrusion genes, likely involved respectively in malate and citrate secretion. Two APase genes encoding putative secreted enzymes were also upregulated. All Pi transporter genes except PHO1;6H were stably expressed, whereas PHO1;6H was significantly upregulated in high-C-secreting roots. Our findings highlight putative genes potentially involved in Pi mobilization, offering insights into plant adaptation to P deficiency.

Salt stress significantly affects plant growth and productivity; therefore, it is important to understand the molecular mechanisms underlying salt tolerance. Myosin XI, a primary driver of intracellular trafficking and organelle movement in plant cells, has recently been implicated in abiotic stress responses. However, their specific roles in salt tolerance remain unclear. In this study, we demonstrate that the expression of Arabidopsis myosin XI isoforms AtXI-K, AtXI-2, and AtXI-1 is induced under salt stress. Notably, both the triple mutant (3ko) and the single atxi-1 mutant showed enhanced salt tolerance. Contrastingly, the salt tolerance of atxi-k, atxi-2, and the double mutant (2ko) lines was similar to that of the wild-type (WT) plants, indicating a specific role of AtXI-1 in salt tolerance. Moreover, the atxi-1 plants accumulated less Na+ and maintained higher chlorophyll and proline contents under salt stress compared to the WT plants. However, reduced seed germination in 3ko under salt stress suggests a stage-specific tolerance mechanism. Hence, AtXI-1 significantly regulates adaptation to salt stress, potentially through the Na+ homeostasis. These findings suggest functional diversification among myosin XI isoforms and provide valuable insights into myosin XI-mediated stress responses, identifying potential targets for enhancing crop resilience to salinity.

The orchid perianth typically consists of three sepals and three petals, with the median petal transformed into a distinct structure lip. In our previously found P code model in orchids, A/E protein OAGL6 interacting with B proteins to form L (OAGL6-2/OAP3-2/OPI) and SP (OAGL6-1/OAP3-1/OPI) complexes in determining lip and sepal/petal identities. This study demonstrates that OAGL6-1 and OAGL6-2 function redundantly with the E-class genes PaSEP1/3 in regulating sepal/petal and lip identities. Single-virus-induced gene silencing (VIGS) of OAGL6-1 resulted in mild morphological alterations in sepals/petals, while silencing PaSEP1 or PaSEP3 individually caused little to no effect. However, triple silencing of OAGL6-1/PaSEP1/PaSEP3 led to additive and severe phenotypes, including greenish sepals/petals with leaf-like epidermal features, indicating a collapse of the SP complex. Similarly, triple silencing of OAGL6-2/PaSEP1/PaSEP3 resulted in the transformation of the lip into a leaf-like structure, demonstrating their redundant roles in lip specification through the advanced L complex. Protein interaction assays confirmed strong interactions between OAGL6-1/2 and PaSEP1/3, supporting the formation of novel, advanced SP and L complexes. Additionally, PaSEP1 and PaSEP3 contribute to pedicel abscission and anthocyanin pigmentation, although their effects are weaker compared to OAGL6-1. Collectively, these findings highlight OAGL6-1 and OAGL6-2 as central regulators of perianth identity through interactions with PaSEP1/3 in the SP and L complexes, respectively. PaSEP1/3 function as minor yet essential partners that help maintain distinct floral organ identities and prevent reversion to leaf-like characteristics. This work expands the P code model and deepens our understanding of the unique mechanisms governing perianth specification in orchids.

Salinity stress is a major environmental factor that limits plant growth and productivity. Understanding the mechanisms of plant salt tolerance is crucial for improving crop yields in saline soils. The Respiratory Burst Oxidase Homologs (Rboh) gene family triggers the production of reactive oxygen species, which act as a signaling molecule to regulate plant tolerance and development under saline conditions. However, a comprehensive analysis of the Rboh gene family in halophytic plants is largely unexplored. In this study, we characterized members of the Rboh gene family in Paspalum vaginatum, a typical halophyte. Evolutionary analysis revealed numerical differences in Pvrboh genes compared to those related species. Additionally, cis-acting elements related to plant hormones, light response, and plant development were identified in Pvrboh promoters. All Pvrboh genes were found to be membrane-localized and upregulated under high salinity, contributing to either root-sourced or leaf-sourced H2O2 production. Gene structural analysis and Ca2+ inhibitor experiments further indicated that Pvrboh4 and Pvrboh5 were closely associated with Ca2+ signaling, whereas Pvrboh6 did not exhibit such an association. Split-luciferase assay in N. benthamiana showed that PvRBOH5 strongly interacted with AtCPK5. Furthermore, a gene regulatory network analysis revealed multiple transcription factors from 32 distinct families that may regulate Pvrboh5 expression. These findings provide new insights into the role of Pvrboh genes in enhancing plant salt tolerance, offering potential targets for improving stress resilience in crops.

Methylorubrum extorquens DSM13060 (Rhizobiales) has a specific capacity to live inside cells of bud meristems in pine trees. The bud niche is almost completely unstudied, although likely widespread in plants. It is unknown how the endosymbiotic methylotroph enters such crucial tissues of the plant. We hypothesized the bud colonization to occur mainly through the shoot epidermis enabled by host-produced methanol. We combined several microscopic methods to illustrate spatio-temporal colonization dynamics and methanol utilization by M. extorquens DSM13060 during the interaction. Our results showed that the endosymbiont mainly enters pine seedlings through cylindrical sheath, which is a layer of living cells surrounding primary root and transition zone. The cylindrical sheath played a central role in accumulation and proliferation of bacteria before entering deeper tissues. The endosymbiont also penetrated host through epidermis and stomatal apertures in stem and formed infection pocket-like structures upon entry. M. extorquens DSM13060 activated the mxaF-promoter on plant surfaces for methanol assimilation prior to shifting to the endosymbiotic lifestyle. Our results suggest that the surface-bound methanol was used for production of antioxidants that enable tissue penetration, documented earlier. Gradual cell-to-cell passage or formation of intracellular infection threads enabled the invasion past endodermis into the xylem. The xylem was observed to function as the main route to the apical meristem, where bacteria were present after 90 days of inoculation. Our study widens the previously known niches and reveals unique and rhizobia-like colonization mechanisms by the endosymbiont in the above and belowground parts of pine.

Vascular bundles, composed of various cell types, are essential for the transport of water and various molecules throughout the plant body. Transcriptional complexes consisting of LONESOME HIGHWAY (LHW) and TARGET OF MONOPTEROS5 regulate vascular development, particularly in two aspects: vascular cell proliferation, which increases the number of vascular cell files, and xylem differentiation in the Arabidopsis root. LHW has three homologs: LHW-LIKE 1 (LL1), LHW-LIKE 2 (LL2), and LHW-LIKE 3 (LL3). In our previous study, we demonstrated that LL1 predominantly contributes to xylem differentiation together with LHW, while its involvement in vascular cell proliferation appears to be limited. The involvement of homologs other than LHW in vascular cell proliferation remains unknown, despite the critical importance of vascular cell proliferation in the initial process of vascular development. Therefore, we investigated the roles of LL2 and LL3 in vascular cell proliferation in this study. Although single loss-of-function mutants of ll2 and ll3 did not exhibit obvious phenotypes, the lhw ll3 double mutant displayed severe defects in root vascular development. In lhw ll3 roots, only one or a few vascular cells were formed, where phloem differentiation was observed but xylem differentiation was absent. In addition, introducing LL3 into lhw could rescue the lhw phenotype. These results suggest that LL3 has a redundant role with LHW in root vascular cell proliferation, and that both LHW and LL3 are essential regulators for this process. Thus, our work indicates that different LHW homologs contribute to distinct functions of LHW in root vascular development.