Plant Communications最新文献

Bacterial pathogens and most nitrogen-fixing rhizobia employ type III effectors (T3Es) as potent tools to manipulate plant signaling pathways, thereby facilitating infection and colonization. However, how rhizobial T3Es regulate legume symbiosis remains elusive. Here, we show that NopM, a T3E from Sinorhizobium fredii NGR234, contributes to infection and nodulation in Lotus japonicus Gifu. The loss of nopM in an NGR234ΔnopT mutant reduced infection and nodulation in L. japonicus, and expression of NopM under the control of L. japonicus NIN promoter enhanced these processes. NopM associated with the NF receptors NFR1 and NFR5 and physically interacted with their cytosolic domains in vitro, and selectively mediated ubiquitination of NFR5. Expression of NopM in hairy roots of NFR5-HA transgenic plants correlated with increased NFR5 protein abundance relative to the inactive NopM variant. Taken together, our work suggests that NopM-dependent effects on symbiosis are associated with increased NFR5 abundance, expanding our understanding of rhizobial T3E functionality and the co-evolution of legume-rhizobium symbiosis.

Aesculus wilsonii, a medicinal tree used in Traditional Chinese Medicine, is rich in aescin and other structurally diverse triterpenoids, yet the biosynthetic mechanism of this diversity remains poorly understood. In this study, we employed integrated omics analyses and functional characterization to elucidate triterpenoid biosynthesis in A. wilsonii. Metabolic profiling annotated 135 triterpenoids that were classified into nine skeleton types, including one previously uncharacterized scaffold. A near telomere-to-telomere genome assembly together with seven transcriptomes enabled comprehensive analysis of genome organization and evolution and determined four triterpenoid biosynthetic gene clusters (TBGC-1 to TBGC-4). Comparative genomics and co-expression analyses identified A. wilsonii-specific cytochrome P450 genes. The functional characterization of seven in yeast together with β-amyrin synthase and cytochrome P450 reductase revealed two CYP716A enzymes from TBGC-2 that catalyzed distinct oxidative reactions. AwCYP716A1278 converted 2,3-oxidosqualene to 21β-hydroxyl-β-amyrin, whereas AwCYP716A277 produced 28-hydroxyl-β-amyrin and oleanolic acid, two oleanane-type triterpenoids. Molecular docking and mutational analyses revealed amino acid residues critical for product specificity. Moreover, functional characterization of a neofunctionalized oxidosqualene cyclase, AwOSC13 from TBGC-4, uncovered a unknown pathway leading to hop-17(21)-en-3β-ol and an uncharacterized triterpenoid. Structural elucidation using NMR and MS identified this compound as moretenol. Heterologous expression of AwOSC13 in tobacco successfully reconstituted the pathway in planta. Together, these findings reveal how biosynthetic gene clusters and enzyme diversification shape triterpenoid metabolism in A. wilsonii and provide valuable resources for discovering and engineering bioactive plant natural products.

Chloroplast biogenesis is essential not only for photosynthesis but also for the synthesis of many metabolites critical for plant growth and human nutrition. Leaf variegation provides a powerful model for dissecting the process of chloroplast biogenesis, which encompasses both chloroplast development and division. Here, we show that the Arabidopsis thaliana leaf variegation mutant var2, defective in the thylakoid protease FtsH2, exhibits severe defects in chloroplast biogenesis. Confocal and ultrastructural analyses revealed that chloroplast development is delayed yet prolonged in the green sectors of var2, leading to increased cellular heterogeneity in chloroplast number and size. Strikingly, plastid-free cells were observed in white sectors, indicating impaired chloroplast division. Consistent with this, loss of the chloroplast division factors Paralog of Accumulation and Replication of Chloroplasts 6 (PARC6) or Plastid Division 1 (PDV1) exacerbated var2 variegation, whereas overexpression of PDV1 or PDV2 suppressed it. Similarly, chloroplast division was compromised in the variegated mutant immutans, whereas the virescent mutant clpr4, which exhibits increased chloroplast number, rescued leaf variegation phenotype of var2. Furthermore, VAR2-regulated chloroplast development and division are mediated by Constitutively Photomorphogenic 1 (COP1) and autophagy-related ATG8a, respectively. Collectively, our findings demonstrate that leaf variegation arises from simultaneous defects in chloroplast development and division, unveiling a coordinated regulatory mechanism that maintains chloroplast homeostasis.

Cadmium (Cd) accumulation in rice grains presents a serious risk to human health; however, the mechanisms underlying this process remain incompletely understood. In this study, a genome-wide association analysis identified 29 loci associated with grain Cd content (LAGCCs). Among these, one of the most strongly associated loci, LAGCC4, contains the transporter gene OsPT1, whose haplotypes show a strong correlation with Cd content in rice grains. A transposon, H-MITE, inserts into the 5' untranslated region (UTR) of OsPT1, altering its expression pattern and leading to increased Cd accumulation. Furthermore, we identified the transcription factor OsbHLH35, which specifically binds to the OsPT1^H-MITE promoter to regulate its transcription in response to Cd stress. Targeted knockout of either OsPT1^H-MITE or OsbHLH35 via CRISPR-Cas9 gene editing significantly reduced grain Cd content, with reductions ranging from 61.7% to 80.6%. This study reveals a previously unrecognized mechanism contributing to high Cd accumulation in rice and identifies genetic targets for breeding rice varieties with reduced Cd content.

Genes that introgress between species can influence the evolutionary and ecological fate of recipients exposed to novel environments. However, key questions on the patterns and molecular mechanisms of introgression in perennial herbaceous plants, which enable distantly related invasive species to thrive in extreme habitats, remain largely unanswered. Here, we report unidirectional introgression from the local species Dendrobium huoshanense to the distantly related invasive species Dendrobium catenatum (Dendrobium officinale) in lithophytic habitats of eastern China. The introgressed regions, which comprise approximately 1% of the genome, contain genes that regulate responses to drought, cold, and metal-ion stresses. Notably, introgressed loci such as CDPK, HHP, PIF, BRI1, and FY show distinct selection signatures and differential expression compared with their paralogs, each playing a distinct role in drought and cold-stress responses. In addition, CIPK23, PDR9, and HAM demonstrate differential expression relative to their paralogous genes and alleles within introgressed loci, indicating their potential involvement in responses to metal-ion stress. Introgression thus facilitates the colonization of arid, metal-enriched sedimentary habitats by D. catenatum. These findings enhance our understanding of Orchidaceae evolution and reveal the evolutionary role of unidirectional introgression in the adaptation of perennial herbaceous plants to extreme environments.

Increasing the dynamics of non-photochemical quenching (NPQ) under changing light levels represents a promising strategy for improving photosynthetic light-use efficiency for greater crop yields. PsbS plays a crucial role in modulating both the capacity and dynamics of NPQ. Nevertheless, the specific mechanisms by which PsbS mediates functional state transitions and the detailed molecular interactions involved in NPQ are still not fully understood. In this study, we identified an amino acid residue, P132, in Arabidopsis thaliana PsbS (AtPsbS) whose substitution with alanine (P132A) causes rapid NPQ induction under low light and significantly reduces the rate of NPQ relaxation in the dark. Our findings suggest that the AtPsbS_P132A mutation keeps PsbS in a loose dimer state that is prone to dissociation and hence causes a reduced proportion of dimers and altered NPQ dynamics. Our study also shows that the AtPsbS_{P132A+E122Q+E226Q} mutant, which lacks protonation-sensing amino acids, may partially induce NPQ even in the absence of protonation, indicating that the structural features of PsbS may independently influence NPQ. Data from this study provide strong evidence that the structural features of PsbS affect NPQ induction and point to a significant role of the PsbS sequence in NPQ dynamics, in addition to the commonly assumed importance of PsbS levels and protonation of E122 and E226 in PsbS. In other words, the protonation sites (i.e., E122 and E226) and the amino acid residues that alter the structural characteristics of the PsbS protein both have an important effect on its NPQ function.