The Role of Plant Hormone Auxin in Leaf Elongation

Plants require auxin, a growth-regulating hormone, to develop leaves. Leaves are initiated when auxin is transported to an area of high concentration in the meristem. Auxin accumulation is influenced by kinases called ERECTA family receptors (ERfs) in an unknown manner. ERf receptors are localized in the plasma membrane, and they are activated by Epidermal Patterning Factor-Like (EPFL) ligands. Whether the ERf receptors are nonfunctional or EPFL 1, 2, 4, and 6 ligands are absent, the number of leaf primordia is drastically reduced and those primordia that form are short. In this project, we measured the height of leaf primordia in Arabidopsis Thaliana mutants lacking different combinations of EPFLs, investigating which EPFLs were most critical in leaf elongation. We discovered that the epfl 1,2 mutant had the shortest leaf primordia, suggesting that EPFL 1 and 2 are the most important for regulating leaf elongation. Auxin is important for leaf growth. This led us to investigate how altering auxin concentrations and transport would affect leaf elongation in EPFL mutants. Wild-type and mutant seedlings were treated exogenously with auxin, an inhibitor of auxin biosynthesis, and with an inhibitor of auxin transport. Altered responses of mutants to described treatments allowed us to build the model of auxin’s role in leaf elongation.