Light- and auxin -regulated protein kinases from Arabidopsis thaliana

Abstract

The WAG1 and WAG2 genes of Arabidopsis thaliana encode protein-serine/threonine kinases that are closely related to PINOID. In order to better understand the roles of WAG1 and WAG2, their gene expression profiles were analyzed. Promoter fusions to the gusA reporter gene demonstrate that the spatial patterns of the WAG promoter acitivity are partially overlapping in young seedlings and mature plants. WAG1 and WAG2 expression was analyzed after treatment with light or exogenously applied phytohormones by RT-PCR. Expression of WAG1 and WAG2 is repressed by light and the plant hormone cytokinin in young seedlings. The hormones auxin, brassinolide, and gibberellin increased WAG mRNAs but the changes were subtle. In order to determine what roles WAG1 and WAG2 play in seedling development, a reverse genetics approach was used to study the wagl, wag2 and wag1/wag2 mutant phenotypes for clues. Although the wag mutants do not contain detectable amounts of the corresponding mRNA, they are wild type in most respects. However, wag1/wag2 double mutants exhibit a pronounced wavy root phenotype when grown vertically on agar plates, a phenotype observed in wild type plants only on plates inclined to angles less than 90°. The wag1 and wag2 mutants also demonstrate enhanced root waving, but to a lesser extent. The double mutant roots are more resistant to the effects of the auxin transport inhibitor N-1-naphthylphthalamic acid on the inhibition of root curling. Moreover, the auxin responsive reporter DR5:GUS is more active in wag1-1/wag2-1 roots than wild type roots raising the possibility that transport of auxin is affected in the wag mutants. The wag1-1/wag2-1 mutant was crossed with mutants affected in gravitropism, auxin transport, auxin signaling, and auxin biosynthesis. From these studies, a model was proposed to describe how these processes interact during root waving