MKP1 acts as a key modulator of stomatal development

Abstract

The MAPK signaling cascade is universal among eukaryotes and mediates a variety of environmental and developmental responses. Two Arabidopsis MAPKs, MPK3 and MPK6, have been shown to be activated by various stimuli and suggested as a convergence point of different signaling pathways. It is known that these MAPKs, MPK3/MPK6, control the discrete stages of stomatal development in Arabidopsis, but how they are regulated and how the same MAPK components can achieve signaling specificity is largely unknown. We recently demonstrated that MAP Kinase Phosphatase 1 (MKP1) promotes stomatal differentiation by suppressing activation of MPK3/MPK6 in the stomatal lineage. By expressing MKP1 in discrete stomatal precursor cell types, we further identified that MKP1 plays an important role at the early stage of stomatal development for the cell fate transition leading to stomatal differentiation. While MKP1 was previously known as a key regulator of environmental stress responses, our data illustrate a novel role of MKP1 in plant development: it acts as one of the specificity-determining regulators of MAPK signaling to enforce proper stomatal development in Arabidopsis.

Keywords: MAPK signaling; MKP1; stomatal development.

Figure 1.

MKP1 is a positive regulator of stomatal development, independent of previously known ecotype-specific developmental defects. (a) Representative confocal images of ten-day-old abaxial rosette leaf epidermis from wild-type (Col), mkp1 (Col), wild-type (Ws), and mkp1 (Ws). Both mkp1 (Col) and mkp1 (Ws) mutants exhibit similar stomatal development defects (reduction of stomata and clusters of small cells, indicated by brackets). Cells were outlined by propidium iodide staining (cyan), and images were taken under the same magnification. Scale bar = 30 µm. (b) Abaxial cotyledon stomatal index of ten-day-old seedlings, expressed as the percentage of the number of stomata to the total number of epidermal cells. n = 10 for each genotype. Bars, means. Error bars, s.e.m.**, P< .001 by Student’s t test. (c) Representative confocal images of five-week-old abaxial rosette leaf (top) and four-week-old stem epidermis (bottom) from wild-type Ws and mkp1 (Ws). Cells were outlined by propidium iodide staining (cyan), and images were taken under the same magnification. Scale bars, 50 μm.

Figure 2.

Transcript levels of stomata-related genes in mkp1(Col) mutants. Ten-day-old seedlings were used for qRT-PCR analysis. Data were collected from three biological replicates, and the expression fold changes were normalized to the transcript level in wild-type (Col). Error bars represent standard deviations (n = 3). Significant difference compared with Col: *P< .01 by Student’s t test.