Fig. 5. STOMAGEN is important for the HY5-mediated promotion of stomatal development.

a–g Light-induced stomatal development is impaired in mutants of STOMAGEN. Arabidopsis seedlings of WT, amiR-stomagen (knockdown line of STOMAGEN), and the overexpressor of STOMAGEN (STOMAGEN-OX) were grown for 10 days under either low (40 µmol m⁻² s⁻¹) or high (160 µmol m⁻² s⁻¹) light intensity. Representative images (a–f) and stomatal indices (g) of the respective abaxial cotyledons are shown. h–l Suppression of the stomatal overproduction phenotype of HY5-OX in a knockdown mutant of stomagen. Arabidopsis seedlings of WT, HY5-OX, amiR-stomagen, and the double-mutant HY5-OX amiR-stomagen were grown for 10 days under 100 µmol m⁻² s⁻¹ of light. Representative images (h–k) and stomatal indices (l) of the respective abaxial cotyledons are shown. Stomata are pseudo-colored in green (a–f, h–k). Scale bar, 80 μm. (m) Gene expression analysis of STOMAGEN in WT, HY5-OX, amiR-stomagen and HY5-OX amiR-stomagen by RT-qPCR. RNA was extracted from 3-day-old seedlings grown under 100 µmol m⁻² s⁻¹ of light. Values are mean + /− SEM, n = 10 independent cotyledons (g, l) or three biological replicates (m). Two-way (g) or one-way (l, m) ANOVA with Tukey’s multiple comparisons test, P < 0.01 (g, l) and P < 0.05 (m). n Model of the HY5-STOMAGEN module in promoting light-mediated stomatal development. Light suppresses COP1 and leads to HY5 accumulation. In mesophyll, HY5 binds and induces STOMAGEN. Increased production of STOMAGEN in turn inhibits the repressive signaling pathway of the epidermal stomatal lineage, leading to the accumulation of SPCH and enhanced stomatal production.