Plant Cell最新文献

Transposon silencing via RNA-directed DNA methylation (RdDM) is mediated primarily through 24-nucleotide (nt) small interfering RNAs (siRNAs) and two plant-specific RNA polymerases, Pol IV and Pol V. We generated and characterized RNA-interference (RNAi) lines targeting the largest subunit of Pol IV and Pol V and the second-largest subunit shared by Pol IV and Pol V in soybean. Our analyses showed that the canonical roles of Pol IV and Pol V in RdDM as described in Arabidopsis, whereby Pol IV produces 24-nt siRNAs and Pol V recruits siRNAs to homologous loci to trigger DNA methylation, are conserved in soybean. Our analyses also uncovered functions of Pol IV and Pol V in that they repress defense response genes en masse. These genes normally undergo RdDM and are silenced, but they are de-repressed when Pol IV and Pol V are knocked down. Furthermore, the de-repression of a set of defense-related genes channeled their RNAs into the RNAi pathway to produce 21-22-nt siRNAs. Knocking down Pol IV and Pol V either singly or together led to increased resistance against the oomycete pathogen Phytophthora sojae, suggesting that Pol IV- and Pol V-mediated gene silencing regulates plant immunity.

Apoplastic acidification represents a pivotal mechanism in the co-evolutionary dynamics between plants and pathogens. However, the mechanisms underlying this process remain largely uncharacterized. In this study, we unveil a mechanism by which the stripe rust fungal (Puccinia striiformis f. sp. tritici; Pst) effector manipulates plasma membrane (PM) H+-ATPases to promote apoplastic acidification and attenuate host immune responses. We identified a wheat (Triticum aestivum) PM H+-ATPase (TaHA2) as a key regulator of apoplastic pH and defense responses to Pst infection. The overexpression of TaHA2 exacerbated apoplastic acidification and Pst susceptibility, whereas the CRISPR-Cas9-mediated inactivation of TaHA2 in wheat conferred broad-spectrum resistance against multiple rust pathogens without compromising agronomic traits. Mechanistically, we found that the wheat calcineurin B-like interacting protein kinase 9 (TaCIPK9) phosphorylates TaHA2 at Ser-933, triggering intramolecular interactions between its C-terminal autoinhibitory domain and the central loop, thereby suppressing TaHA2 activity. Conversely, the CFEM (common in fungal extracellular membrane)-containing Pst effector PstCFEM2 competitively binds to the C-terminus of TaHA2, disrupting TaCIPK9-mediated phosphorylation and relieving autoinhibition. This effector-driven activation of TaHA2 amplifies apoplastic acidification and stomatal opening, ultimately dampening plant immunity. Our findings reveal a mechanism by which pathogens promote infection by subverting host pH regulation and provide a theoretical framework for engineering disease resistance through the manipulation of susceptibility genes.

As an important agronomic trait that directly determines grain yield, seed size is tightly controlled by the timing of endosperm cellularization and seed coat proliferation. However, the precise regulatory mechanisms that coordinate the two processes remain elusive. Here, we demonstrate that in Arabidopsis (Arabidopsis thaliana), CINCINNATA (CIN)-like TEOSINTE BRANCHED 1/CYCLOIDEA/PCF (TCP) transcription factors are crucial for seed size by controlling both endosperm cellularization and seed coat growth. Disruption of TCP function in the triple mutant tcp3/4/10 causes enlarged seeds due to the delayed endosperm cellularization and accelerated seed coat growth. TCP4 directly represses MINISEED3 (MINI3) and SHORT HYPOCOTYL UNDER BLUE1 (SHB1), key factors for endosperm cellularization, by recruiting the FERTILIZATION INDEPENDENT SEED-POLYCOMB REPRESSIVE COMPLEX 2 (FIS-PRC2) complex. TCP4 also interacts with MINI3 to repress MINI3-SHB1 complex activity, thereby suppressing the expression of MINI3 downstream genes. We further show that TCP4 represses the expression of AINTEGUMENTA (ANT), a key regulator of integument and seed coat growth, by directly binding to its promoter. Our findings demonstrate that CIN-like TCPs play critical roles in controlling seed size by promoting endosperm cellularization and concurrently inhibiting seed coat proliferation.

RNA uridylation is a pervasive mechanism that regulates the degradation of eukaryotic mRNAs. In Arabidopsis (Arabidopsis thaliana), uridylation influences mRNA decay by favoring 5' to 3' degradation and by preventing excessive deadenylation. Yet, the significance of mRNA uridylation during plant development remains largely unknown. Here, we adapted FLEP-seq2, a method based on nanopore sequencing, to generate a comprehensive inventory of mRNA uridylation events in different Arabidopsis tissues. We also evaluated the contributions of the two known Arabidopsis uridylyltransferases, UTP:RNA URIDYLYLTRANSFERASE 1 (URT1) and HEN1 SUPPRESSOR1 (HESO1), in mRNA uridylation. Our transcriptome-wide analysis showed that URT1 is the main enzyme responsible for mRNA uridylation in all analyzed tissues, while HESO1 can marginally uridylate mRNAs. Importantly, our results revealed the singularity of mRNA uridylation pattern in seeds and the dual function of URT1-dependent uridylation in shaping the transcriptome during seed maturation. We propose that during the late stages of seed maturation, URT1-dependent uridylation facilitates the degradation of unnecessary mRNAs encoding translation-related proteins, while promoting the accumulation of mRNAs associated with the maturation program, by hindering their deadenylation. In line with its important function in shaping the seed transcriptome, our study also identifies URT1 as a regulator of seed dormancy. Overall, our study reveals the biological relevance of mRNA uridylation during the late stages of seed maturation.

PcG proteins play a crucial role in the regulation of eukaryotic development. Two major complexes, PRC1/2, are responsible for H2Aub and H3K27me3, respectively. While the core composition of PRC2 is conserved across species and its activity is required for gene repression, PRC1 components are diverse, and the role of H2Aub is not yet fully understood. In Arabidopsis (Arabidopsis thaliana), both B-cell-specific Moloney murine leukemia virus integration site 1 (BMI1A/B/C) and Really Interesting New Gene 1 (RING1A/B) display H2Aub activity, but whether any link or difference exists between RING1 and BMI1 proteins' in vivo activity in Arabidopsis remains unknown. Here, we show that the catalytic activities of RING1 and BMI1 proteins, rather than their mere presence, are required for gene regulation. We found that BMI1 affects the H2Aub on both H2Aub/H3K27me3- and only-H2Aub-marked genes, whereas genes marked only by H2Aub largely depend on RING1A/B. Our data also show specific subsets of genes in which H3K27me3 levels are partially maintained by the RING-domain proteins independently of their catalytic activities, and other subsets of genes where BMI1s assist RING1s' activities for H2Aub marking, highlighting their unique and common functions.

Primary root growth, regulated by internal hormone signals, adapts to external factors such as water availability, soil compactness, and microbial interactions. An essential step in root growth consists of cell divisions in the meristem, with the outermost root cap layer thought to provide protection. However, recent studies reveal that lateral root cap (LRC) cells control meristem size and lateral root initiation. In this study, we identified an upper LRC-specific protein condensation mechanism involving SUPPRESSOR of rps4-RLD1 (SRFR1) that governs root growth and show that growth conditions and hormone treatment dynamically modulate condensate accumulation. SRFR1 condensate formation is driven by its plant-associated N-terminal tetratricopeptide repeat (PANT) polymerization domain and fine-tuned by the adjacent intrinsically disordered region 1 (IDR1). Mutational and biophysical analyses show that IDR1's zwitterionic nature is essential for its regulatory role, acting as a chaperone to promote PANT polymerization at low temperatures while preventing aggregation at high temperatures. This enables SRFR1 condensate formation across a wide temperature range. Notably, the zwitterionic IDR1 can be functionally substituted by zwitterionic dehydrins. Shifting IDR1 toward a negative state impairs, whereas a positive shift enhances SRFR1 condensation and further improves root growth. The association of zwitterionic IDRs with polymerization domains is common, suggesting that this mechanism broadly prevents irreversible aggregation and promotes physiological polymerization under varying temperatures.