Further characterization of auxin-regulated mRNAs in hypocotyl sections of mung bean [Vigna radiata (L.) Wilczek]: sequence homology to genes for fatty-acid desaturases and atypical late-embryogenesis-abundant protein, and the mode of expression of the mRNAs

Abstract

The amino-acid sequence deduced from the nucleotide sequence of an auxin-regulated gene, ARG1, isolated from auxin-treated sections of mung-bean hypocotyls (Yamamoto et al. 1992, Plant Cell Physiol. 33, 13-20), is 69% identical to that of a delta 15 fatty-acid desaturase from Brassica napus L. that is localized in the endoplasmic reticulum. The ARG1 message is present at high levels in the hook portion of the hypocotyl, the plumule and the root tip of 3-d-old etiolated seedlings. The amino-acid sequence encoded by another auxin-regulated gene, ARG2, is 39% identical to that of an atypical late-embryogenesis-abundant (LEA) protein of cotton, LEA5-A. The ARG2 message is localized in the upper part of hypocotyls. Its abundance increases upon treatment of hypocotyl sections with fusicoccin, as well as with auxin. Determination of the distribution and kinetics of induction of mRNAs transcribed from the five auxin-regulated genes of mung bean, which include Aux22s and SAUR as well as ARG1 and ARG2, shows that they are heterogeneous in their mode of gene expression. The physiological implications of the homology between the two auxin-regulated genes and the genes for previously identified proteins are discussed in the context of auxin-induced elongation of the hypocotyl.