Abstract
Compensation is a phenomenon observed in mutants and transgenics that have a severe defect in cell proliferation in leaf primordia, where the leaf-cell expansion is aberrantly enhanced. This suggests that there are some intrinsic mechanisms which coordinates cell proliferation and cell expansion during leaf development. To elucidate the mechanism of compensation, we isolated several xs mutants that have a specific defect in cell expansion. Through the genetical analyses between xs and a compensation-exhibiting mutant, angustifolia3 (an3), we found that some of xs mutations clearly suppress aberrant cell enlargement in an3. For further analysis, we focused on xs2 that has the most significant defect in cell expansion among them. Positional cloning revealed that XS2 encodes a member of cation calcium exchanger proteins. Interestingly, genes involved salicylic-acid (SA) signaling were expressed much higher in xs2 compared to WT. In addition to it, exogenous SA supply clearly suppressed aberrant cell enlargement in an3. These indicated that the excessive SA-mediated response caused by xs2 mutation is somehow involved in suppression of compensated cell enlargement in an3.
