Search

Background: The NAC family of transcription factors is one of the largest gene families of transcription factors in plants and the conifer NAC gene family is at least as large, or possibly larger, as in Arabidopsis. These transcription factors control both developmental and stress induced processes in plants. Yet, conifer NACs controlling stress induced processes has received relatively little attention. This study investigates NAC family transcription factors involved in the responses to the pathogen Heterobasidion annosum (Fr.) Bref. sensu lato., Results: The phylogeny and domain structure in the NAC proteins can be used to organize functional specificities, several well characterized stress-related NAC proteins are found in III-3 in Arabidopsis (Jensen et al. Biochem J 426:183-196, 2010). The Norway spruce genome contain seven genes with similarity to subgroup III-3 NACs. Based on the expression pattern PaNAC03 was selected for detailed analyses. Norway spruce lines overexpressing PaNAC03 exhibited aberrant embryo development in response to maturation initiation and 482 misregulated genes were identified in proliferating cultures. Three key genes in the flavonoid biosynthesis pathway: a CHS, a F3'H and PaLAR3 were consistently down regulated in the overexpression lines. In accordance, the overexpression lines showed reduced levels of specific flavonoids, suggesting that PaNAC03 act as a repressor of this pathway, possibly by directly interacting with the promoter of the repressed genes. However, transactivation studies of PaNAC03 and PaLAR3 in Nicotiana benthamiana showed that PaNAC03 activated PaLAR3A, suggesting that PaNAC03 does not act as an independent negative regulator of flavan-3-ol production through direct interaction with the target flavonoid biosynthetic genes., Conclusions: PaNAC03 and its orthologs form a sister group to well characterized stress-related angiosperm NAC genes and at least PaNAC03 is responsive to biotic stress and appear to act in the control of defence associated secondary metabolite production.

The plant GT43 protein family includes xylosyltransferases that are known to be required for xylan backbone biosynthesis, but have incompletely understood specificities. RT-q PCR and histochemical ( GUS) analyses of expression patterns of GT43 members in hybrid aspen, reported here, revealed that three clades of the family have markedly differing specificity towards secondary wall-forming cells (wood and extraxylary fibres). Intriguingly, GT43 A and B genes (corresponding to the Arabidopsis IRX9 clade) showed higher specificity for secondary-walled cells than GT43 C and D genes ( IRX14 clade), although both IRX9 and IRX14 are required for xylosyltransferase activity. The remaining genes, GT43 E, F and G ( IRX9- L clade), showed broad expression patterns. Transient transactivation analyses of GT43 A and B reporters demonstrated that they are activated by Ptxt MYB021 and PNAC085 (master secondary wall switches), mediated in Ptxt MYB021 activation by an AC element. The high observed secondary cell wall specificity of GT43 B expression prompted tests of the efficiency of its promoter ( p GT43 B), relative to the Ca MV 35 S ( 35 S) promoter, for overexpressing a xylan acetyl esterase ( CE5) or downregulating REDUCED WALL ACETYLATION ( RWA) family genes and thus engineering wood acetylation. CE5 expression was weaker when driven by p GT43 B, but it reduced wood acetyl content substantially more efficiently than the 35 S promoter. RNAi silencing of the RWA family, which was ineffective using 35 S, was achieved when using GT43 B promoter. These results show the utility of the GT43 B promoter for genetically engineering properties of wood and fibres. [ABSTRACT FROM AUTHOR]