ABSTRACT: rs04-03_myb - myb - Xylogenesis is a fundamental developmental process that is specific of vascular plants. It allows the formation of xylem, also called wood in trees, a complex tridimensional tissue composed of different cell types. This process occurs through the control of fundamental cell mechanisms like cell division and differentiation, secondary cell wall synthesis, lignin deposition and programmed cell death. Xylogenesis is controlled spatially and temporally by specific genetic programs that involve hundreds of genes. For instance, lignin biosynthetic genes, CAD and CCR, are specifically expressed during xylogenesis through MYB transcription factor binding sites, a process that seems to be common to all vascular plants. We have cloned two xylem specific MYB transcription factors, EgMYB1 et EgMYB2, in Eucalyptus. Interestingly, they are able to bind MYB consensus sequences of CAD and CCR promoters in vitro and to modulate CAD and CCR expression in vivo. When overexpressed in Arabidopsis or tobacco, they affect xylem structure by changing cell wall structure and quality. To follow expression changes of Arabidopsis genes in transgenic plants overexpressing Eg MYB1 and EgMYB2 should help us to find out which genes might be target of those transcription factors. This should help us to decipher the actual role of those two MYBs in xylogenesis, two new members of a large family of transcription factors in plants. - Xylogenesis is a fundamental developmental process that is specific of vascular plants. It allows the formation of xylem, also called wood in trees, a complex tridimensional tissue composed of different cell types. This process occurs through the control of fundamental cell mechanisms like cell division and differentiation, secondary cell wall synthesis, lignin deposition and programmed cell death. Xylogenesis is controlled spatially and temporally by specific genetic programs that involve hundreds of genes. For instance, lignin biosynthetic genes, CAD and CCR, are specifically expressed during xylogenesis through MYB transcription factor binding sites, a process that seems to be common to all vascular plants. We have cloned two xylem specific MYB transcription factors, EgMYB1 et EgMYB2, in Eucalyptus. Interestingly, they are able to bind MYB consensus sequences of CAD and CCR promoters in vitro and to modulate CAD and CCR expression in vivo. When overexpressed in Arabidopsis or tobacco, they affect xylem structure by changing cell wall structure and quality. To follow expression changes of Arabidopsis genes in transgenic plants overexpressing Eg MYB1 and EgMYB2 should help us to find out which genes might be target of those transcription factors. This should help us to decipher the actual role of those two MYBs in xylogenesis, two new members of a large family of transcription factors in plants. Keywords: gene knock in (transgenic)
