AtMYB7, a new player in the regulation of UV-sunscreens in Arabidopsis thaliana

The phenylpropanoid metabolic pathway provides a wide variety of essential compounds for plants. Together with sinapate esters, in Brassicaceae species, flavonoids play an important role in protecting plants against UV irradiation. In this work we have characterized Arabidopsis thaliana AtMYB7, the closest homolog of AtMYB4 and AtMYB32, described as repressors of different branches of phenylpropanoid metabolism. The characterization of atmyb7 plants revealed an induction of several genes involved in flavonol biosynthesis and an increased amount of these compounds. In addition, AtMYB7 gene expression is repressed by AtMYB4. As a consequence, the atmyb4 mutant plants present a reduction of flavonol contents, indicating once more that AtMYB7 represses flavonol biosynthesis. Our results also show that AtMYB7 gene expression is induced by salt stress. Induction assays indicated that AtMYB7 represses several genes of the flavonoid pathway, DFR and UGT being early targets of this transcription factor. The results obtained indicate that AtMYB7 is a repressor of flavonol biosynthesis and also led us to propose AtMYB4 and AtMYB7 as part of the regulatory mechanism controlling the balance of the main A. thaliana UV-sunscreens.This work was supported by the Spanish ‘Ministerio de Economía y Competitividad’ [AGL2011-30545-C02-01 to D.C.-R.]; the Spanish Ministerio de Ciencia e Innovación [CONSOLIDER-INGENIO program (CSD2007-00036)]; Autonomous Government of Catalonia [grant AGAUR (2008FI-B 00399) to J.E.S.-H.]; CRAG [a contract to J.E.S.-H.]. This work was carried out within the framework of the ‘Xarxa de Referència de Biotecnologia’ (XarBa) from the Autonomous Government of Catalonia.Peer reviewe