MAP3Kδ4, an Arabidopsis Raf-like MAP3K, regulates plant growth and shoot branching

Abstract

MAP3Kδ4 (At4g23050) is a Raf-like mitogen-activated protein kinase kinase kinase (MAP3K) in Arabidopsis thaliana, classified as subgroup B2. The B2 subgroup MAP3Ks have a kinase domain in the C-terminus and a PAS domain in the N-terminal region. PAS domains are found in a variety of proteins and are reported to mediate protein–protein interactions and to sense environmental stimuli. However, the function of MAP3Kδ4 has not yet been determined. We generated transgenic plants constitutively expressing MAP3Kδ4 or its kinase-negative mutant (MAP3Kδ4KN) and characterized their physiological traits. The transgenic plants overexpressing MAP3Kδ4 showed earlier bolting than wild-type plants. They also showed more vigorous growth by both fresh weight and stem length. In contrast, the transgenic plants overexpressing MAP3Kδ4KN showed a highly branched phenotype; MAP3Kδ4 overexpression had no effect on branch number. These results indicated that MAP3Kδ4 is crucial to regulating both plant growth and shoot branching. In addition, MAP3Kδ4 transcripts were found in all Arabidopsis tissues examined and upregulated by auxin treatment in seedlings, suggesting that MAP3Kδ4 functions in an auxin-dependent manner.