Transcriptomic analyses reveal common heterophylly regulations in eight amphibious eudicots

Heterophylly, the ability of plants to produce various leaf forms in response to environments, is widely seen in nature. Aquatic plants emerged from various lineages of land plants, and amphibious species are those that can survive in both terrestrial and submerged conditions. In this study, we conducted phenotypical studies and transcriptomic analyses of eight amphibious eudicots. We quantified leaf shape changes under terrestrial and submerged conditions and found that dissection index (DI) is a proper indicator to quantify leaf complexity among heterophyllous species. We identified groups of differentially expressed genes (DEGs) related to heterophylly, mainly in terms of leaf shape, stomata development, and phytohormone biosynthesis. Different heterophyllous species have diverse regulations of leaf shape and we verified the function of candidate class I KNOTTED1-LIKE HOMEOBOX (KNOX1) genes using transgenic Arabidopsis lines. Stomatal densities are commonly decreased under water and genes related to its development are also downregulated. Abscisic acid (ABA) may be a key factor regulating heterophylly, and CATALASE genes are upregulated under submergence. Our study uncovered common and special characteristics among eight amphibious eudicots, providing resources to reveal mechanisms of heterophylly and convergent evolutions.