CO₂ Sensitivity is Suppressed by ht1, a Mutant Arabidopsis Gene Encoding a Protein Kinase

Abstract

Arabidopsis ht1 was isolated as a hot phenotype under low CO₂ concentration. Its stomatal response to CO₂ was significantly inhibited. The mutated HT1 gene was speculated to encode a protein kinase. To determine whether the HT1 proteins have a phosphorylation activity, we performed in vitro kinase assay. The data indicated that the HT1 has both autophosphorylation and phoshprylation activity. ht1-1 has a mutation site which converts R to K residue within the catalytic subdomain VIb. This conversion greatly impaired the phosphorylation activity in vitro. We constructed a kinase negative mutant of HT1 gene, in which the lysine codon at the predicted ATP-binding site was replaced by a tryptophan codon (HT1:KW). Over expression of the HT1:KW in normal plants results in suppression of the sensitivity to CO₂. These results indicate that the HT1 kinase plays an important role in the CO₂ signaling.