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Summary: Drought stress has detrimental effects on plants. Although the abscisic acid (ABA)‐mediated drought response is well established, defensive mechanisms to cope with dehydration‐induced proteotoxicity have been rarely studied. DRR1 was identified as an Arabidopsis drought‐induced gene encoding an ER‐localized RING‐type E3 Ub ligase. Suppression of DRR1 markedly reduced tolerance to drought and proteotoxic stress without altering ABA‐mediated germination and stomatal movement. Proteotoxicity‐ and dehydration‐induced insoluble ubiquitinated protein accumulation was more obvious in DRR1 loss‐of‐function plants than in wild‐type plants. These results suggest that DRR1 is involved in an ABA‐independent drought stress response possibly through the mitigation of dehydration‐induced proteotoxic stress. [ABSTRACT FROM AUTHOR]

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]

Summary: Oryza sativa BRASSINAZOLE RESISTANT 1 (OsBZR1) is the closest rice homolog of the Arabidopsis BZR1 and bri1‐EMS‐SUPPRESSOR 1 (BES1)/BZR2 transcription factors. OsBZR1 plays a central role in the rice brassinosteroid signaling pathway. Despite its functional importance, the control mechanism by which the cellular stability of OsBZR1 is regulated has not yet been fully elucidated. Here, we report that a rice U‐box E3 ubiquitin (Ub) ligase OsPUB24 acts as a negative regulator in the BR signaling pathway via the 26S proteasome‐dependent degradation of OsBZR1. The ospub24 T‐DNA knock‐out mutant and Ubi:RNAi‐OsPUB24 knock‐down rice plants displayed enhanced seedling growth, increased lamina joint bending, and hypersensitivity to brassinolide (BL). The expressions of the BR biosynthetic genes suppressed by BR in a negative feedback loop were lower in the mutant progeny than in the wild‐type rice plants, which indicated increased BR responses in the mutant line. OsPUB24 ubiquitinated OsBZR1, resulting in the proteasomal degradation of OsBZR1. In addition, the stability of OsPUB24 was downregulated by BL and bikinin, an inhibitor of Oryza sativa Shaggy/GSK3‐like kinase 22 (OsSK22). OsSK22, the homolog of Arabidopsis BRASSINOSTEROID INSENSITIVE 2 (BIN2) protein kinase, phosphorylated OsPUB24 and elevated the cellular stability of OsPUB24. Our findings suggest that OsPUB24 participates in OsBZR1 turnover, and that the regulatory networks of OsPUB24, OsSK22 and OsBZR1 are crucial for fine‐tuning the BR response in rice. Significance Statement: OsBZR1 transcription factor is a key component of the rice brassinosteroid signaling pathway. Here, we show that OsBZR1 is subject to control by two negative factors, OsSK22 protein kinase and OsPUB24 E3 ubiquitin ligase, in the rice BR signaling pathway. This study illustrates that the signaling process of BR is cooperatively regulated by two distinct types of post‐translational modifications, phosphorylation and ubiquitination. [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]