Functional Analysis of the Arabidopsis thaliana CDPK-Related Kinase Family: AtCRK1 Regulates Responses to Continuous Light

Abstract

The Calcium-Dependent Protein Kinase (CDPK)-Related Kinase family (CRKs) consists of eight members in <i>Arabidopsis</i>. Recently, At<i>CRK5</i> was shown to play a direct role in the regulation of root gravitropic response involving polar auxin transport (PAT). However, limited information is available about the function of the other At<i>CRK</i> genes. Here, we report a comparative analysis of the <i>Arabidopsis</i> CRK genes, including transcription regulation, intracellular localization, and biological function. At<i>CRK</i> transcripts were detectable in all organs tested and a considerable variation in transcript levels was detected among them. Most AtCRK proteins localized at the plasma membrane as revealed by microscopic analysis of 35S::cCRK-GFP (Green Fluorescence Protein) expressing plants or protoplasts. Interestingly, 35S::cCRK1-GFP and 35S::cCRK7-GFP had a dual localization pattern which was associated with plasma membrane and endomembrane structures, as well. Analysis of T-DNA insertion mutants revealed that At<i>CRK</i> genes are important for root growth and control of gravitropic responses in roots and hypocotyls. While At<i>crk</i> mutants were indistinguishable from wild type plants in short days, At<i>crk1-1</i> mutant had serious growth defects under continuous illumination. Semi-dwarf phenotype of At<i>crk1-1</i> was accompanied with chlorophyll depletion, disturbed photosynthesis, accumulation of singlet oxygen, and enhanced cell death in photosynthetic tissues. At<i>CRK1</i> is therefore important to maintain cellular homeostasis during continuous illumination.