Possible regulation of Arabidopsis MYB93 by both SCARECROW and MPK3.

The promoter of the Arabidopsis MYB93 ( MYB93 ) transcription factor was previously identified in a large-scale screen using the SCARECROW ( SCR ) transcription factor. Independent high-throughput studies also identified MYB93 as a protein-interaction partner of the MAP kinase 3 ( MPK3 ). Here, we validate and extend those observations using RT-PCR, yeast two-hybrid assays and phenotypic analysis. MYB93 transcript levels were elevated in the scr-3 mutant and reduced upon expression of SCR-GFP, indicating regulation by SCR. In yeast, the N-terminal domain of MYB93 , but not the C-terminal region, interacted with MPK3 . We also observed that mpk3-1 mutants exhibited a lateral root phenotype similar to myb93-1 . Together, these findings support a model in which both MYB93 gene expression and MYB93 protein function are modulated by SCR and MPK3 , respectively.