Overexpression of PaNAC03, a stress induced NAC gene family transcription factor in Norway spruce leads to reduced flavonol biosynthesis and aberrant embryo development

Abstract

BackgroundThe 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.ResultsThe 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0952-8) contains supplementary material, which is available to authorized users.

Transcriptional Factors Regulate Plant Stress Responses Through Mediating Secondary Metabolism

“…Flavonoids accumulation in Norway spruce (Picea abies) increased the resistance against the fungal pathogen Heterobasidion annosum [129]). Recently, it was revealed that PaNAC03 responded against infection of H. annosum by negatively regulating some flavonoid biosynthetic genes, such as CHS, F3'H, and LAR3 [107]. Moreover, ANACO32 has also been identified as a negative regulator of anthocyanin biosynthesis.…”

Regulation of stilbene biosynthesis in plants

“…Other transcription factors, apart from R2R3-MYBs and bHLHs, e.g., Basic Leucine Zipper Domain (bZIP) or NAC, have been reported as positive regulators of flavonoid biosynthesis (Morishita et al 2009;Malacarne et al 2016). The single repeat MYBs (R3-MYBs), squamosa promoter binding protein like (SPL), or some NAC TFs, have been reported as negative regulators of flavonoid biosynthesis in plants (Dubos et al 2008;Gou et al 2011;Dalman et al 2017). The R3-MYB and SPL are known to repress flavonoid biosynthesis by disrupting the formation of the MYBbHLH-WD40 complexes.…”

A class B heat shock factor selected for during soybean domestication contributes to salt tolerance by promoting flavonoid biosynthesis

“…Previously, MYB, bHLH and WD40 proteins have been found to regulate flavonoid biosynthesis by governing the expression of flavonoid synthesis genes (Lotkowska et al ., ). In addition, NAC‐type, WRKY‐type, MADS‐type and bZIP‐type transcriptional factors have also been identified as regulators of the flavonoid biosynthesis pathway (Jaakola et al ., ; Amato et al ., ; Dalman et al ., ; Lloyd et al ., ). Here, we found that soybean NAC‐type transcription factor GmNAC2 is a direct negative modulator of flavonoid biosynthesis.…”