Lit Lunch 3-27-13 Role and Interrelationship of GaProtein, Hydrogen Peroxide, and Nitric Oxide in Ultraviolet B-Induced Stomatal Closure in Arabidopsis Leaves

Heterotrimeric G proteins have been shown to transmit ultraviolet B (UV-B) signals in mammalian cells, but whether they alsotransmit UV-B signals in plant cells is not clear. In this paper, we report that 0.5 Wm22 UVB induces stomatal closure inArabidopsis(Arabidopsis thaliana) by eliciting a cascade of intracellular signaling events including Gaprotein, hydrogen peroxide (H2O2), and nitric oxide (NO). UV-B triggered a significant increase in H2O2 or NO levels associated with stomatal closure in the wild type, but these effects were abolished in the single and double mutants of AtrbohDandAtrbohFor in theNia1mutants, respectively. Furthermore, we found that UV-B-mediated H2O2 and NO generation are regulated by GPA1, the Ga-subunit of heterotrimeric G proteins. UV-B-dependent H2O2 and NO accumulation were nullified ingpa1knockout mutants but enhanced by overexpression of a constitutively active form ofGPA1(cGa). In addition, exogenously applied H2O2or NO rescued the defect in UV-B-mediated stomatal closure ingpa1mutants, whereas cGaAtrbohD/AtrbohFand cGania1constructs exhibited a similar response toAtrbohD/AtrbohF and Nia1, respectively. Finally, we demonstrated that Gaactivation of NO production depends on H2O2. The mutants of AtrbohDandAtrbohFhad impaired NO generation in response to UV-B, but UV-B-induced H2O2accumulation was not impaired in Nia1. Moreover, exogenously applied NO rescued the defect in UVB-mediated stomatal closure in the mutants of AtrbohDand AtrbohF.Thesefindings establish a signaling pathway leading to UV-B-induced stomatal closure that involves GPA1-dependent activation of H2O2 production and subsequent Nia1-dependent NO accumulation.