Analysis of HT1 protein kinase involved in stomatal CO₂ response

Abstract

Arabidopsis ht 1 was isolated as a hot phenotype under low CO₂ concentration. Its stomatal response to CO₂ was significantly inhibited. The mutated HT1 gene encodes a protein kinase expressed in stomatal guard cells. Phosphorylation assays demonstrate that HT1 has both autophosphorylation and phoshprylation activity. HT1 protein carrying the ht 1-1 or ht 1-2 mutation is greatly impaired or abolished, respectively. The kinase activities of the WT HT1 and its two mutants corresponded nicely to the phenotypes observed in whole plants. Dominant negative transgenic plants in which HT1 kinase activity was disrupted showed suppressed sensitivity to CO₂. These results indicate that the HT1 kinase plays an important role in the CO₂ signaling. Furthermore, in the ht 1 mutants, ABA responses were comparable to those of WT plants. This suggests that the HT1 kinase would function in CO₂ signaling pathway independent of ABA signaling.