DROUGHT INDUCED FUNCTION OF ARABIDOPSIS CPK8 IN DOWN REGULATING ATCAT3 IN GUARD CELLS

Abstract

Drought is a major threat for all terrestrial plants. The movement of guard cells in stomatal complexes controls water loss and uptake of CO2 for photosynthesis. The cytosolic free Ca2+ elevated in guard cells in response to stress stimuli triggers stomatal closure. The plant specific calcium-dependent protein kinases (CDPKs) play important roles in regulating downstream components of calcium signalling. This study aimed to characterize CPK8 gene, its function and interactive protein in response to drought stress. Results revealed that T-DNA insertion mutant of CPK8 was more sensitive to drought stress than wild-type plants. The GUS staining studies confirmed that CPK8 expressed in leaves, specifically in guard cells. RT-PCR analysis showed that CPK8 expression was induced in response to drought stress. The Arabidopsis catalase 3 (CAT3) was identified as the CPK8-interacting protein through yeast two hybrid screening. The CAT3 knockout (cat3) plants displayed similar drought sensitive phenotype as cpk8 plants. The GUS staining and RT-PCR analysis showed that CAT3 also expressed in seedlings, leaves and particularly in guard cells suggesting possible interaction with CPK8. The transient expression of 35Spro:CPK8-GFP and 35Spro:CAT3 GFP in the mesophyll protoplasts of Arabidopsis showed that both proteins were localized in the plasma membrane. When treated with ABA, both cpk8 and cat3 mutants showed enhanced production of H2O2 in stomatal guard cells and rosette leaves compared with wild type plants. All these results suggested that CPK8 and CAT3 involve in plant signalling in responses to drought stress by participating in Ca2+-, ABA and H2O2-mediated stomatal regulation.