439회 From genomics to cellular dynamics: ABA and calcium signaling in …

439회 

연사:  곽준명, University of Maryland

제목: From genomics to cellular dynamics: ABA and calcium signaling in guard cells

Abstract 

The phytohormone abscisic acid (ABA) regulates diverse cellular processes including modulation of seed dormancy, seed maturation, stomatal movements, gene expression, and vegetative growth during plant development. Reactive oxygen species (ROS) and the gas nitric oxide (NO) are short-lived molecules and act as as second messengers to mediate ABA signaling in stomatal guard cells. Previously, we showed that two NADPH oxidases AtrbohD and AtrbohF are responsible for ABA-triggered ROS production and act as positive regulators of guard cell ABA signaling. Recently, we have identified two MAP kinase genes that are highly and preferentially expressed in guard cells and act downstream of ROS to positively regulate ABA- and calcium-activation of anion channels and ABA-induced stomatal closure. Furthermore, using a biochemical and proteomics approach, we demonstrated that the ABA-activated OST1 protein kinase that functions upstream of the NADPH oxidases by phosphorylating AtrbohF, which is responsible for the production of reactive oxygen species (ROS) in response to ABA in order to mediate ABA signaling in guard cells.

In animals, ionotropic glutamate receptors are ligand-gated ion channels and function as neurotransmitter receptors that mediate synaptic excitation in the central nervous system, and thus play a crucial role in long-term memory. The Arabidopsis genome encodes 20 glutamate receptor homolog genes (AtGLRs) that are divided into 3 phylogenetically distinct subfamilies. Several studies with pharmacological blockers and genetic mutants have suggested that Arabidopsis glutamate receptor homologs have a role in light signaling, calcium fluxes, cell division and survival in roots, carbon and nitrogen metabolism, ABA biosynthesis, responses to aluminum or environmental stress, calcium homoeostasis, and resource allocation. Despite all these findings, direct proof of AtGLR protein function has not yet been provided. Using a heterologous expression system, we have identified AtGLRs that form calcium-permeable ion channels. Our data indicate that these AtGLRs are localized to the plasma membrane and physically interact with each other. Analysis of atglr genetic mutants demonstrates that these proteins function in calcium-mediated cellular signaling and growth processes. Further progress will be discussed.