As abscisic acid (ABA) receptors, PYR1/PYL/RCAR (PYLs) play important roles in ABA-mediated seed germination, but the regulation of PYLs in this process, especially at the transcriptional level, remains unclear. In this study, we found that expression of 11 of 14 PYLs changes significantly during seed germination and is affected by exogenous ABA. Two PYLs, PYL11 and PYL12, both of which are expressed specifically in mature seeds, positively modulate ABA-mediated seed germination. However, ABI5 was found to modulate the PYL11-and PYL12-mediated ABA response. In the abi5-7 mutant, ABA hypersensitivity caused by PYL11 and PYL12 overexpression was totally or partially blocked. By contrast, ABI5 regulates the expression of PYL11 and PYL12 by directly binding to their promoters. Moreover, the expression of eight other PYLs is also affected during the germination of abi5 mutants. Promoter analysis revealed that an ABI5binding region is present next to the TATA box or initiator box. Together, our data demonstrate the role of PYL11 and PYL12 in seed germination. In addition, the identification of PYLs as targets of ABI5 reveals a role of ABI5 in the feedback regulation of ABA-mediated seed germination.

 Plant stomata are crucial to control water transpiration in response to environmental stresses and to modulate gas exchange necessary for photosynthesis. The phytohormone ABA promotes stomatal closure and inhibits light-induced stomatal opening. The Arabidopsis thaliana E3 ubiquitin ligase COP1 functions in ABA-mediated stomatal closure. However, the underlying molecular mechanisms are still not fully understood.  Yeast two-hybrid assays were used to identify ABA signaling components that interact with COP1, and biochemical, molecular and genetic studies were carried out to elucidate the regulatory role of COP1 in ABA signaling.  The cop1 mutants are hyposensitive to ABA-triggered stomatal closure under light and dark conditions. COP1 interacts with and ubiquitinates the Arabidopsis thaliana Clade A type 2C phosphatases (PP2Cs) ABI/HAB group and AHG3, thus triggering their degradation. ABA enhances the COP1-mediated degradation of these PP2Cs. Mutations in ABI1 and AHG3 partly rescue the cop1 stomatal phenotype and the phosphorylation level of OST1, a crucial Accepted Article This article is protected by copyright. All rights reserved SnRK2-type kinase in ABA signaling.  Our data indicate that COP1 is part of a novel signaling pathway promoting ABA-mediated stomatal closure by regulating the stability of a subset of the Clade A PP2Cs. These findings provide novel insights into the interplay between ABA and the light signaling component in the modulation of stomatal movement.

Summary In response to pathogens, plant cells exhibit a rapid increase in the intracellular calcium concentration and a burst of reactive oxygen species (ROS). The cytosolic increase in Ca2+ and the accumulation of ROS are critical for inducing programmed cell death (PCD), but the molecular mechanism is not fully understood. We screened an Arabidopsis mutant, sad2‐5, which harbours a T‐DNA insertion in the 18th exon of the importin beta‐like gene, SAD2. The H2O2‐induced increase in the [Ca2+]cyt of the sad2‐5 mutant was greater than that of the wild type, and the sad2‐5 mutant showed clear cell death phenotypes and abnormal H2O2 accumulation under fumonisin‐B1 (FB1) treatment. CaCl2 could enhance the FB1‐induced cell death of the sad2‐5 mutant, whereas lanthanum chloride (LaCl3), a broad‐spectrum calcium channel blocker, could restore the FB1‐induced PCD phenotype of sad2‐5. The sad2‐5 fbr11‐1 double mutant exhibited the same FB1‐insensitive phenotype as fbr11‐1, which plays a critical role in novo sphingolipid synthesis, indicating that SAD2 works downstream of FBR11. These results suggest the important role of nuclear transporters in calcium‐ and ROS‐mediated PCD response as well as provide an important theoretical basis for further analysis of the molecular mechanism of SAD2 function in PCD and for improvement of the resistance of crops to adverse environments.

Water shortage is a global challenge and affects crop growth and development seriously. Stoma is the main channel of plant water transpiration. Water transpiration through stomata is an endothermic process and affects temperature of plants, especially leaf surface. In this study, we established a method for screening maize seedling mutant with abnormal leaf temperature by far infrared imaging. We found that seedling mutants with abnormal leaf temperature manifested different drought tolerance. Mutants with lower leaf temperature demonstrated faster moisture loss rate, poorer drought tolerance, higher osmotic potential, lower leaf relative water content, more accumulation of hydrogen peroxide, more serious cell membrane damage and more robust root systems and biomass under drought treatment, which are opposite in maize seedling mutants with higher leaf surface temperature compared with the corresponding control. Taken together, the method we established is an effective way to screen maize mutants with abnormal drought response.

Seed germination is a physiological process regulated by multiple factors. Abscisic acid (ABA) can inhibit seed germination to improve seedling survival under conditions of abiotic stress, and this process is often regulated by light signals. Constitutive photomorphogenic 1 (COP1) is an upstream core repressor of light signals and is involved in several ABA responses. Here, we demonstrate that COP1 is a negative regulator of the ABA-mediated inhibition of seed germination. Disruption of COP1 enhanced Arabidopsis seed sensitivity to ABA and increased reactive oxygen species (ROS) levels. In seeds, ABA induced the translocation of COP1 to the cytoplasm, resulting in enhanced ABA-induced ROS levels. Genetic evidence indicated that HY5 and ABI5 act downstream of COP1 in the ABA-mediated inhibition of seed germination. ABA-induced COP1 cytoplasmic localization increased HY5 and ABI5 protein levels in the nucleus, leading to increased expression of ABI5 target genes and ROS levels in seeds. Together, our results reveal that ABA-induced cytoplasmic translocation of COP1 activates the HY5-ABI5 pathway to promote the expression of ABA-responsive genes and the accumulation of ROS during ABAmediated inhibition of seed germination. These findings enhance the role of COP1 in the ABA signal transduction pathway.