Cloning and functional analysis of two flavanone-3-hydroxylase genes from Reaumuria trigyna

Reaumuria trigyna is a highly xeric small shrub and is a rare wild plant in Mediterranean areas. The flavonoid biosynthesis pathway in R. trigyna is strongly activated under salt stress, and many genes related to this pathway showed significant differences in transcript abundance under salt stress in a previous transcriptomic profiling analysis. The F3H gene, which encodes flavanone-3-hydroxylase, is an essential gene in the flavonoid biosynthetic pathway. The transcript levels of two F3H genes, RtF3H1 and RtF3H2, were increased in R. trigyna not only under salt stress but also under drought and cold stresses, and by abscisic acid. We measured the transcript levels of the two genes in different organs. There were high transcript levels of RtF3H1 in stems, and high transcript levels of RtF3H2 in roots and stems. The full-length cDNAs for RtF3H1 (Accession No. AB850638) and RtF3H2 (Accession No. AB850639) were cloned and were found to encode 353- and 358-amino-acid proteins, respectively. Escherichia coli overexpressing RtF3H1 or RtF3H2 showed better growth than that of a control E. coli line under various stress treatments. The survival rate of the recombinant E. coli strain expressing RtF3H2 was higher than that of the strain expressing RtF3H1 under salt and drought stresses.