Overexpression of a basic helix-loop-helix gene Antagonist of PGL1 (APG) decreases grain length of rice

Abstract

Previously we reported that three basic helix-loop-helix (bHLH) protein dimers are involved in regulating grain length of rice. Two atypical bHLH proteins named Positive regulator of grain length i (PGL1) and PGL2 positively regulate grain length in transgenic rice when they are overexpressed in lemma/palea. Their interaction partner Antagonist of PGL1 (APG), a typical bHLH, is assumed to have opposite function. Suppression of APG expression level by RNAi increased grain length significantly. Here, we report further evidence that APG is a negative regulator of grain length in rice. Overexpression of APG resulted in short grain. Inner epidermal cell layer of lemma from APG overexpression lines showed reduced cell length. Taken together, the results illustrated the biological role of a typical bHLH APG as a negative regulator of rice grain length that controls cell elongation. © 2012 The Japanese Society for Plant Cell and Molecular Biology.