Plant Communications最新文献

Ethylene signaling is one of the classic hormonal pathways in plants, with diverse roles in development and stress responses. The dimeric ethylene receptor localizes to the endoplasmic reticulum and contains Cu(I) ions essential for ethylene binding and signal transduction. We previously discovered that mutants of the Arabidopsis gene POLARIS (PLS), encoding a 36-amino-acid peptide, exhibit enhanced ethylene signaling responses suggestive of reduced receptor activity, but the role and activity of the PLS peptide in this signaling cascade have not been defined. Here, we report that Arabidopsis PLS binds copper as a 1:2 thiol-dependent Cu(I):PLS₂ complex with an affinity of 3.79 (±1.5) × 10¹⁹ M^-2 via two cysteine residues conserved in the related species Camelina sativa. These residues are also essential for biological function. This affinity precludes a role for PLS as a cytosolic Cu chaperone. We demonstrate that PLS localizes to endomembranes and interacts with the transmembrane domain of the receptor protein ETR1. PLS-ETR1 binding is increased in the presence of copper, and this interaction provides a Cu-dependent mechanism for mediating the repression of ethylene responses. Because PLS transcription is upregulated by auxin and downregulated by ethylene, PLS-ETR1 interactions also provide a mechanism for modulation of ethylene responses in high-auxin tissues.

A substantial but largely unexplored fraction of eukaryotic proteomes is composed of peptides and small proteins (the peptidome). In recent years, short open reading frames (sORFs) capable of encoding functional peptides have been identified within transcripts annotated as non-coding RNAs or in intergenic regions. These sORF-encoded peptides (SEPs) were previously overlooked due to their small size and difficulties in detection, both experimentally and computationally. However, analyses of translating RNAs (ribosome profiling) and proteomics (mass spectrometry) have provided growing evidence for the existence of numerous novel 'non-conventional' peptides in eukaryotic organisms, including plants. In animals, mounting evidence indicates that long non-coding RNAs are an important source of SEPs, and that SEPs participate in crucial cellular and physiological processes and can mediate the evolution of novel characteristics. Similar findings are now emerging in plants. The SEP-coding capacity and the full repertoire of functional SEPs within eukaryotic genomes remain unclear, but systematic, large-scale molecular screenings are beginning to address this gap. Here, we review current progress in understanding the plant non-conventional peptidome, explore parallels between plants and animals, and illustrate how findings in animals can help guide plant research on this topic.

Phenylethanoid glycosides (PhGs) are a group of important natural products widely distributed in medicinal plants and known for their remarkable pharmacological properties. Uridine diphosphate (UDP) glycosyltransferase 79G15 (UGT79G15) from Rehmannia glutinosa catalyzes the conversion of osmanthuside A to osmanthuside B, a key intermediate in the PhG biosynthetic pathway, through the formation of a (1→3) glycosidic bond. In this study, we present the crystal structures of UGT79G15 in its apo form, UDP-bound form, and, notably, its ternary complex containing UDP and a mimic acceptor, forsythiaside A, within its active site. Structural and comparative analyses revealed that UGT79G15 possesses a distinctive funnel-shaped acceptor-binding pocket with a small auxiliary cavity capable of accommodating the 4'-hydroxycinnamoyl group of PhGs, explaining the enzyme's regiospecificity toward the 3'-OH of the acceptor. Additional structural examination and site-directed mutagenesis identified key residues that recognize and stabilize UDP-rhamnose and the sugar acceptor. Among the variants generated, I204W exhibits enhanced catalytic efficiency for osmanthuside A conversion, reaching up to 2.2-fold higher activity than the wild type. This study provides mechanistic insight into the donor specificity and acceptor regioselectivity of PhG 1,3-rhamnosyltransferase and expands the structural understanding of plant UGTs.

The naturally selected extreme traits of zinc and cadmium hyperaccumulation and hypertolerance in Arabidopsis halleri depend on strongly elevated HEAVY METAL ATPase 4 (HMA4) transcript levels compared to those in the closely related Arabidopsis thaliana. This difference is regulated in cis; AhHMA4 upstream sequences alone are sufficient to confer increased expression, as previously demonstrated using reporter gene fusions stably introduced into both A. halleri and A. thaliana. However, the underlying cis-regulatory divergence specific to A. halleri remains unknown. Here, we identify cis-regulatory metal hyperaccumulation elements (MHEs) that increase AhHMA4 promoter activities by examining stably transformed reporter lines carrying partial deletions or mutations in AhHMA4 upstream sequences. MHE1 (consensus TGTAAC) functions in the distal regions of AhHMA4 promoters, and all three tandem AhHMA4 gene copies share a proximal upstream pair of MHE2 motifs (consensus AAATATCT), corresponding to the evening element. The evening element is a known target of Arabidopsis CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1), a core circadian clock transcription factor that mediates light-dependent and circadian gene expression. We show that the elevated activity of the AhHMA4-1 promoter depends on MHE2 in cis and CCA1 in trans, and it can be recapitulated by introducing an intact pair of MHE2 motifs into the A. thaliana HMA4 promoter using site-directed mutagenesis. We also found that HMA4 transcript levels show diel rhythmicity in A. halleri but not in A. thaliana. In summary, we identify the causal cis-regulatory elements that co-opt a known regulator of diel and seasonal transcriptional rhythms to mediate enhanced expression of a gene critical for a naturally selected extreme trait syndrome.

The dissemination of insect-borne plant pathogens relies on their ability to influence vector behavior. Certain bacteria-infected plants exhibit increased attractiveness to vectors; however, the underlying mechanisms remain poorly characterized. Huanglongbing (HLB), a devastating citrus disease, is primarily caused by the bacterium "Candidatus Liberibacter asiaticus" (CLas) and transmitted by psyllid vectors. In this study, we demonstrate that the effector protein SDE5, secreted by CLas, suppresses the biosynthesis of volatile terpenoids in host citrus plants, thereby enhancing psyllid attraction. Biochemically, SDE5 functions as an inhibitor of bacterial C-type lysozyme, facilitating both CLas infection and psyllid vector attraction. Two plant U-box (PUB) E3 ligases, PUB10 and PUB21, are recruited by SDE5 to promote ubiquitination and proteasomal degradation of MYC2, a key transcription factor in jasmonate signaling and terpene-based anti-herbivore defenses. Furthermore, SDE5 interferes with MYC2 dimerization, diminishing its ability to activate terpene biosynthesis genes. This dual suppression markedly reduces volatile terpenoid emissions in SDE5-transgenic citrus lines, resulting in increased psyllid attraction and enhanced psyllid fitness. Conversely, the anti-proteolysis peptide 3-14 (APP 3-14), which stabilizes the MYC2 protein and inhibits the HLB pathogen, enhances volatile terpenoid emission and repels psyllids. These findings provide a novel strategy for disrupting mutualistic interactions between plant bacterial pathogens and insect vectors by modulation of olfactory defense.

Pollen hydration represents the initial and critical step in pollen-stigma interactions and is necessary for successful plant fertilization. The FERONIA (FER) receptor kinase regulates pollen hydration by modulating stigmatic reactive oxygen species (ROS) accumulation through rapid alkalinization factor 23/33 (RALF23/33) and pollen coat protein B-class peptide (PCP-B) signaling. However, the function and regulatory mechanism of FER's receptor kinase activity in pollen hydration remain poorly understood. In this study, we found that the kinase-dead form of FER^K565R fails to restore stigmatic ROS accumulation and pollen hydration in the fer-4 mutant. By integrating RNA sequencing database analyses with yeast two-hybrid assays, we identified three type 2C phosphatases (PP2Cs)-protein phosphatase 2C clade H 1 (PP2CH1) and clade-E Growth-Regulating 1 and 2 (EGR1 and EGR2)-that interact with FER at the plasma membrane. These PP2Cs dephosphorylate FER at Ser695 and Thr696 within the activation segment, thereby inhibiting its kinase activity. Mutations at these two residues reduced ROS levels in the stigma and increased pollen hydration rates. Altogether, this study reveals a crucial regulatory mechanism of FER signaling, demonstrating that PP2CH1, EGR1, and EGR2 act as negative regulators of FER kinase activity to modulate stigmatic ROS accumulation and promote pollen hydration.

This study presents a gap-free, telomere-to-telomere (T2T), cytogenetically integrated genome assembly of eggplant (Smel HQ v.2.0), providing insights into universal and tissue-specific roles of SmeMYBs in anthocyanin biosynthesis. This high-quality reference genome will significantly facilitate future genetic and genomic studies in eggplant.