Dalman Kerstin, Wind Julia Johanna, Nemesio-Gorriz Miguel, Hammerbacher Almuth, Lundén Karl, Ezcurra Ines, Elfstrand Malin
Department of Forest Mycology and Plant Pathology, Uppsala Biocenter, Swedish University of Agricultural Sciences, Uppsala, Sweden.
Department of Chemistry and Biotechnology, Uppsala Biocenter, Swedish University of Agricultural Sciences, Uppsala, Sweden.
BMC Plant Biol. 2017 Jan 6;17(1):6. doi: 10.1186/s12870-016-0952-8.
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.
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.
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.
NAC转录因子家族是植物中最大的转录因子基因家族之一，针叶树的NAC基因家族至少与拟南芥中的一样大，甚至可能更大。这些转录因子控制着植物的发育过程和应激诱导过程。然而，针叶树中控制应激诱导过程的NAC转录因子受到的关注相对较少。本研究调查了参与对病原菌蜜环菌（广义）响应的NAC家族转录因子。
NAC蛋白的系统发育和结构域结构可用于组织功能特异性，在拟南芥的III-3中发现了几种特征明确的与应激相关的NAC蛋白（Jensen等人，《生物化学杂志》426:183-196，2010）。挪威云杉基因组包含七个与III-3亚组NACs相似的基因。基于表达模式，选择了PaNAC03进行详细分析。过表达PaNAC03的挪威云杉品系在成熟起始时表现出异常的胚胎发育，并且在增殖培养物中鉴定出482个调控失调的基因。类黄酮生物合成途径中的三个关键基因：一个CHS、一个F3'H和PaLAR3在过表达品系中持续下调。相应地，过表达品系中特定类黄酮的水平降低，这表明PaNAC03可能通过直接与受抑制基因的启动子相互作用，作为该途径的阻遏物。然而，在本氏烟草中对PaNAC03和PaLAR3的反式激活研究表明，PaNAC03激活了PaLAR3A，这表明PaNAC03并非通过与目标类黄酮生物合成基因直接相互作用，作为黄烷-3-醇产生的独立负调控因子。
PaNAC03及其直系同源物形成了一个与特征明确的与应激相关的被子植物NAC基因的姐妹群，并且至少PaNAC03对生物胁迫有响应，似乎在控制与防御相关的次生代谢产物产生中发挥作用。
