A M yb transcription factor regulates genes of the phenylalanine pathway in maritime pine

• Published in: The Plant journal : for cell and molecular biology 2013-06, Vol.74 (5), p.755-766
• Main Authors: Craven‐Bartle, Blanca, Pascual, Mª Belen, Cánovas, Francisco M., Ávila, Concepción
• Format: Article
• Language: English
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.12158

During the life cycles of conifer trees, such as maritime pine ( P inus pinaster A it.), large quantities of carbon skeletons are irreversibly immobilized in the wood. In energetic terms this is an expensive process, in which carbon from photosynthesis is channelled through the shikimate pathway for the biosynthesis of phenylpropanoids. This crucial metabolic pathway is finely regulated, primarily through transcriptional control, and because phenylalanine is the precursor for phenylpropanoid biosynthesis, the precise regulation of phenylalanine synthesis and use should occur simultaneously. The promoters of three genes encoding the enzymes prephenate aminotransferase ( PAT ), phenylalanine ammonia lyase ( PAL ) and glutamine synthetase ( GS 1b) contain AC elements involved in the transcriptional activation mediated by R 2 R 3‐ M yb factors. We have examined the capacity of the R 2 R 3‐ M yb transcription factors M yb1, M yb4 and M yb8 to co‐regulate the expression of PAT , PAL and GS1b . Only M yb8 was able to activate the transcription of the three genes. Moreover, the expression of this transcription factor is higher in lignified tissues, in which a high demand for phenylpropanoids exits. In a gain‐of‐function experiment, we have shown that M yb8 can specifically bind a well‐conserved eight‐nucleotide‐long AC‐II element in the promoter regions of PAT , PAL and GS1b , thereby activating their expression. Our results show that M yb8 regulates the expression of these genes involved in phenylalanine metabolism, which is required for channelling photosynthetic carbon to promote wood formation. The co‐localization of PAT , PAL , GS1b and MYB 8 transcripts in vascular cells further supports this conclusion.