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SUMMARY: Ubiquitination is a critical post‐translational protein modification that has been implicated in diverse cellular processes, including abiotic stress responses, in plants. In the present study, we identified and characterized a T‐DNA insertion mutant in the At5g10650 locus. Compared to wild‐type Arabidopsis plants, at5g10650 progeny were hyposensitive to ABA at the germination stage. At5g10650 possessed a single C‐terminal C3HC4‐type Really Interesting New Gene (RING) motif, which was essential for ABA‐mediated germination and E3 ligase activity in vitro. At5g10650 was closely associated with microtubules and microtubule‐associated proteins in Arabidopsis and tobacco leaf cells. Localization of At5g10650 to the nucleus was frequently observed. Unexpectedly, At5g10650 was identified as JAV1‐ASSOCIATED UBIQUITIN LIGASE1 (JUL1), which was recently reported to participate in the jasmonate signaling pathway. The jul1 knockout plants exhibited impaired ABA‐promoted stomatal closure. In addition, stomatal closure could not be induced by hydrogen peroxide and calcium in jul1 plants. jul1 guard cells accumulated wild‐type levels of H2O2 after ABA treatment. These findings indicated that JUL1 acts downstream of H2O2 and calcium in the ABA‐mediated stomatal closure pathway. Typical radial arrays of microtubules were maintained in jul1 guard cells after exposure to ABA, H2O2, and calcium, which in turn resulted in ABA‐hyposensitive stomatal movements. Finally, jul1 plants were markedly more susceptible to drought stress than wild‐type plants. Overall, our results suggest that the Arabidopsis RING E3 ligase JUL1 plays a critical role in ABA‐mediated microtubule disorganization, stomatal closure, and tolerance to drought stress. Significance Statement: Ubiquitination is a universal post‐translational protein modification in eukaryotic organisms. We show that Arabidopsis RING E3 ubiquitin ligase JUL1 plays a critical role in ABA‐mediated microtubule disorganization, stomatal closure, and tolerance to drought stress. The present study demonstrates that the ubiquitin‐mediated microtubule structure in guard cell is functionally correlated with ABA‐dependent drought stress response in Arabidopsis. [ABSTRACT FROM AUTHOR]

A highly coordinated complex known as the microprocessor precisely processes primary transcripts of MIRNA genes into mature mi RNAs. In plants, the microprocessor minimally consists of three components: Dicer-like protein 1 ( DCL1), HYPONASTIC LEAF 1 ( HYL1), and SERRATE ( SE). To precisely modulate mi RNA maturation, the microprocessor cooperates with at least 12 proteins in plants. In addition, we here show the involvement of a novel gene, HYL1-interacting GIY- YIG-like endonuclease ( HIGLE). The encoded protein has a GIY- YIG domain that is generally found within a class of homing endonucleases. HIGLE directly interacts with the microprocessor components HYL1 and SE. Unlike the functions of other GIY- YIG endonucleases, the catalytic core of HIGLE has both DNase and RNase activities that sufficiently processes mi RNA precursors into short fragments in vitro. [ABSTRACT FROM AUTHOR]

The multi-pass transmembrane protein ACCELERATED CELL DEATH 6 (ACD6) is an immune regulator in Arabidopsis thaliana with an unclear biochemical mode of action. We have identified two loci, MODULATOR OF HYPERACTIVE ACD6 1 (MHA1) and its paralog MHA1-LIKE (MHA1L), that code for ∼7 kDa proteins, which differentially interact with specific ACD6 variants. MHA1L enhances the accumulation of an ACD6 complex, thereby increasing the activity of the ACD6 standard allele for regulating plant growth and defenses. The intracellular ankyrin repeats of ACD6 are structurally similar to those found in mammalian ion channels. Several lines of evidence link increased ACD6 activity to enhanced calcium influx, with MHA1L as a direct regulator of ACD6, indicating that peptide-regulated ion channels are not restricted to animals. [Display omitted] • ACD6 is a plant Ca2+-conducting channel • MHA1L peptide ligand enhances ACD6-stimulated ion channel activity • MHA1L and ACD6 are required for calcium signaling during PTI The ankyrin-repeat transmembrane protein ACD6 was identified two decades ago, but its exact biochemical function has remained enigmatic. Chen et al. show that ACD6 is a bona fide regulator of calcium influx using heterologous systems and calcium reporters in plants and that this activity can be further enhanced by a MHA1L peptide ligand. [ABSTRACT FROM AUTHOR]

Abstract AtUBC32, AtUBC33, and AtUBC34 comprise Arabidopsis group XIV E2 ubiquitin-conjugating enzymes. Yeast two-hybrid, in vitro pull-down, and bimolecular fluorescence complementation assays revealed that group XIV E2s are interacting partners of the U-box-type E3 ligase PUB19, a negative regulator of drought stress response. These three AtUBCs are co-localized with PUB19 to the punctae-like structures, most of which reside on the endoplasmic reticulum membrane of tobacco leaf cells. Suppression of AtUBC32 , AtUBC33 , and AtUBC34 resulted in increased abscisic acid-mediated stomatal closure and tolerance to drought stress. These results indicate that Arabidopsis group XIV E2s play negative roles in drought stress response. [ABSTRACT FROM AUTHOR]