Partial deficiency of isoleucine impairs alters transcript levels of the genes involved in branched-chain amino acid and glucosinolate metabolism in Arabidopsis

Isoleucine (Ile) is one of the branched-chain amino acids (BCAAs) that are essential substrates for protein synthesis in all organisms. In this study, we characterized an Arabidopsis mutant, lib (low isoleucine biosynthesis), that has defects in both cell proliferation and cell expansion processes during root development. This mutant carries a mutation in OMR1 gene that encodes a threonine deaminase/dehydratase (TD) which results in a defect in isoleucine production. Microarray analysis indicated that the partial deficiency of Ile in the lib mutant triggers a decrease in transcript levels of the genes encoding the major enzymes involved in the BCAA degradation pathway; the analysis also indicated that many genes involved in the biosynthesis of methionine-derived glucosinolates are up-regulated. Total RNAs were isolated from three replicate samples of the root tissues of 8-day-old wild type (w) and lib mutant (m)seedlings grown on 1/2 MS medium and hybridized on Affymetrix ATH1 microarrays. The changes of gene expression in the lib mutant (m) was compared with the wild type (w). The corrected P value of <0.05 was used to select the genes for comparison, and only those genes whose expression was two-fold higher or lower in lib than in the WT were used for analysis.