Biology subjects

Kamiyama, Y.

Publications and source records attributed to Kamiyama, Y..

3 recordsLinked to original sources

bioRxiv2024

MAP4K1 and MAP4K2 regulate ABA-induced and Ca2+-mediated stomatal closure in Arabidopsis

Abscisic acid (ABA)-induced stomatal closure limits water loss from plants under drought stress. To investigate signaling pathways involved in stomatal closure, we performed a phosphoproteomic analysis of ABA-treated Arabidopsis guard cell protoplasts (GCPs). From this analysis, we discovered that MITOGEN-ACTIVATED PROTEIN 4 KINASE 1 (MAP4K1) is phosphorylated in response to ABA. Subsequent biochemical assays showed that Ser-479 of MAP4K1 is directly phosphorylated by SRK2E (OST1/SnRK2.6), a protein kinase that plays a central role in ABA-induced responses. Mutational analyses of MAP4K1, as well as closely related MAP4K2, revealed that both kinases positively regulate ABA-induced stomatal closure, and that Ser-479 of MAP4K1 was required for this phenotype. In map4k1map4k2, stomatal closure was induced by exogenous Ca2+ but not H2O2. Furthermore, electrophysiology experiments showed that MAP4K1/2 are required for ABA-dependent activation of Ca2+-permeable channels in GCPs. Together, our results indicate that SnRK2 and MAP4K1/2 function as a signaling module to regulate Ca2+-mediated stomatal closure.

plant biology↗

bioRxiv2023

Hyperosmolarity-induced suppression of group B1 Raf-like protein kinases modulates drought-growth trade-off in Arabidopsis

When plants are exposed to drought stress, there is a trade-off between plant growth and stress responses. Here, we identified a signaling mechanism for the initial steps of the drought-growth trade-off. Phosphoproteomic profiling revealed that Raf13, a B1 subgroup Raf-like kinase, is dephosphorylated under drought conditions. Raf13 and the related B1-Raf Raf15 are required for growth rather than the acquisition of osmotolerance. We also found that Raf13 interacts with B55-family regulatory subunits of protein phosphatase 2A (PP2A), which mediates hyperosmolarity-induced dephosphorylation of Raf13. In addition, Raf13 interacts with an AGC kinase INCOMPLETE ROOT HAIR ELONGATION HOMOLOG 1 (IREH1), and Raf13 and IREH1 have similar functions in regulating cellular responses that promote plant growth. Overall, our results support a model in which Raf13-IREH1 activity promotes growth under nonstressed conditions, whereas PP2A activity suppresses Raf13-IREH1 during osmotic stress to modulate the physiological "trade-off" between plant growth and stress responses.

plant biology↗

bioRxiv2020

SNF1-related protein kinase 2 directly regulate group C Raf-like protein kinases in abscisic acid signaling

ABSTRUCTA phytohormone abscisic acid (ABA) has a major role in abiotic stress responses in plants, and subclass III SNF1-related protein kinase 2 (SnRK2) mediates ABA signaling. In this study, we identified Raf36, a group C Raf-like protein kinase in Arabidopsis, as an interacting protein with SnRK2. A series of reverse genetic and biochemical analyses revealed that Raf36 negatively regulates ABA responses and is directly phosphorylated by SnRK2s. In addition, we found that Raf22, another C-type Raf-like kinase, functions partially redundantly with Raf36 to regulate ABA responses. Comparative phosphoproteomic analysis using Arabidopsis wild-type and raf22raf36-1 plants identified proteins that are phosphorylated downstream of Raf36 and Raf22 in planta. Together, these results reveal a novel subsection of ABA-responsive phosphosignaling pathways branching from SnRK2.

plant biology↗