Several aquatic or wetland plants including R. trichophyllus, have stomata mostly on the adaxial side. Such an adaxial-side-specific distribution of stomata is named epi-stomy. Epi-stomy is an adaptive strategy for wetland plants because stomata are the entry sites where pathogens infect plants and pathogens invade plants more easily if stomata were located at abaxial side. The molecular mechanism underlying epi-stomy is unknown yet. I hypothesized that epi-stomy in R. trichophyllus is mediated by auxin and leaf polarity genes. Here, I compared the stomatal densities and distributions of R. trichophyllus and 3 of its relative species. R. trichopyllus and R. sceleratus are epi-stomatous while R. japonicus is hypo-stomatous. Then I treated auxin and auxin transport inhibitor, NPA, to R. trichophyllus. Stomatal distribution was significantly altered after the NPA treatment. To elucidate the molecular mechanism regulating stomatal distribution, I cloned R. trichophyllus genes which regulate stomatal development, including RtSTO and RtSPCH. Then I analyzed the spatial expression pattern ofRtSTO and RtSPCH. Both of the genes are expressed specifically on adaxial side. In addition, RtSTO is negatively regulated by auxin. In addition, A. thaliana transformants overexpressing leaf polarity genes of R. trichophyllus showed altered stomatal density and distribution. Based on those findings, I concluded that (1) Auxin and leaf polarity genes function as signals with spatial information (2) Such patial signals induce the differential expression of RtSTO and RtSPCH and epi-stomy.
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