The FOUR LIPS (FLP) and MYB88 genes conditionally suppress the production of nonstomatal epidermal cells in Arabidopsis cotyledons.

Abstract

The Arabidopsis MYB transcriptional factors FOUR LIPS (FLP) and MYB88 are predicted to play a broader role than just limiting the number of guard cells per stoma in the epidermis based on their expression patterns. Analysis of the numbers of all epidermal cells in cotyledons in flp mutants and the flp-1 myb88 double mutant may substantiate the functions of FLP and MYB88 in nonstomatal epidermal cells. The number of all types of abaxial epidermal cells in mature cotyledons were determined under different growth conditions in flp-1, flp-3, flp-8, and tmm-1 single mutants, flp-1 tmm-1 and flp-1 myb88 double mutants, and accessions Columbia-0 (Col, control for flp-1, flp-3, and flp-1 myb88) and Landsberg erecta (Ler, control for flp-8). In soil-grown plants, the number of pavement cells and meristemoids per cotyledon were not statistically different between the flp mutants and their respective controls and between flp-1 and flp-1 myb88, except sometimes for the number of meristemoids or pavement cells between flp-1 and Col. In contrast, the same comparisons yielded statistically significant differences in medium-grown plants, i.e., more cells in the flp mutants and flp-1 myb88, except for meristemoids between flp-8 and Ler and pavement cells between flp-1 and flp-1 myb88. No significant difference was detected for nonstomatal epidermal cells between tmm-1 and flp-1/tmm-1 under the two conditions. FLP and MYB88 inhibit the production of nonstomatal epidermal cells largely in a growth-condition-dependent manner. The tmm-1 mutation is epistatic to the flp-1 mutation in the production of nonstomatal epidermal cells in the cotyledon.