Expression data from overexpressers and mutants of TFs-gene LBD37 and LBD38 under different nitrogen regimes

Nitrogen (N) and nitrate (NO3-) per se regulate many aspects of plant metabolism, growth and development. N/NO3- also suppresses parts of secondary metabolism including anthocyanin synthesis. Molecular components for this repression are unknown. We report that three N/NO3--induced members of the LATERAL ORGAN BOUNDARY DOMAIN (LBD) gene family of transcription factors (LBD37, LBD38 and LBD39) act as negative regulators of anthocyanin biosynthesis in Arabidopsis (Arabidopsis thaliana). Over-expression of each of the three genes in the absence of N/NO3- strongly suppresses the key regulators of anthocyanin synthesis PAP1 and PAP2, genes in the anthocyanin-specific part of flavonoid synthesis, as well as cyanidin- but not quercetin- or kaempferol-glycoside production. Conversely, lbd37, lbd38 or lbd39 T-DNA insertion mutants accumulate anthocyanins when grown in N/NO3--sufficient conditions and show constitutive expression of anthocyanin biosynthetic genes. The LBD genes also repress many other known N-responsive genes including key genes required for NO3- uptake and assimilation, resulting in altered NO3- content, nitrate reductase activity/activation, protein, amino acid and starch levels, and N-related growth phenotypes. The results identify LBD37 and its two close homologs as novel repressers of anthocyanin biosynthesis and N-availability signals in general. They also show that besides being developmental regulators LBD genes fulfill roles in metabolic regulation. We used microarrays to test whether LBD37 and LBD38 have a more widespread role in NO3-/N-regulation. 9-day old Arabidopsis seedlings were harvested for RNA extraction and hybridization on Affymetrix microarrays. Total RNA was prepared separately from three biological replicates of N-limited LBD37OX, LBD38OX and WT seedlings, and N-replete lbd37-1 mutant, lbd38 mutant and WT seedlings (18 samples).