Two differentially regulated Arabidopsis genes define a new branch of the DFR superfamily

Two tandem genes were identified on Arabidopsis chromosome II (AtCRL1 and A tCRL2) encoding proteins with homology to members of the dihydroflavunol-4- reductase (DFR) superfamily. The encoded CRL1 and CRL2 proteins share 87% m utual amino acid sequence identity whereas their promoter regions are highl y divergent, suggesting differential regulation of the CRL genes, Phylogene tic analysis placed CRL1 and CRL2 in a separate branch of the DFR superfami ly. Northern blotting showed strong AtCRL1 induction by abscisic acid (ABA) , drought, and heat shock, and high expression level in seeds: thus resembl ing the expression pattern of late embryogenic abundant ABA-responsive gene s. Differential expression of the two genes during plant development was co nfirmed in plants expressing transcriptional fusions between the two promot ers and the Escherichia coli P-glucuronidase reporter gene. This showed tha t, whereas high expression of AtCRL1 in mature seeds declines during subseq uent vegetative growth, transcriptional activity from the AtCRL2 promoter i ncreases during vegetative growth. Expression of both genes is restricted t o vascular tissue. Based upon their homology to proteins involved in lignin synthesis, we propose that ArCRL2 is involved in generating conducting tis sue late in development, while AtCRL1 is involved in vascular tissue differ entiation and/or synthesis in the germinating embryos. (C) 2001 Elsevier Sc ience Ireland Ltd. All rights reserved.