The HvNAC6 transcription factor: a positive regulator of penetration resistance in barley and Arabidopsis

Abstract

Pathogens induce the expression of many genes encoding plant transcription factors, though specific knowledge of the biological function of individual transcription factors remains scarce. NAC transcription factors are encoded in plants by a gene family with proposed functions in both abiotic and biotic stress adaptation, as well as in developmental processes. In this paper, we provide convincing evidence that a barley NAC transcription factor has a direct role in regulating basal defence. The gene transcript was isolated by differential display from barley leaves infected with the biotrophic powdery mildew fungus, Blumeria graminis f.sp. hordei (Bgh). The full-length cDNA clone was obtained using 5'-RACE and termed HvNAC6, due to its high similarity to the rice homologue, OsNAC6. Gene silencing of HvNAC6 during Bgh inoculation compromises penetration resistance in barley epidermal cells towards virulent Bgh. Complementing the effect of HvNAC6 gene silencing, transient overexpression of HvNAC6 increases the occurrence of penetration resistant cells towards Bgh attack. Quantitative RT-PCR shows the early and transient induction of HvNAC6 in barley epidermis upon Bgh infection. Additionally, our results show that the Arabidopsis HvNAC6 homologue ATAF1 is also induced by Bgh and the ataf1-1 mutant line shows decreased penetration resistance to this non-host pathogen. Collectively, these data suggest a conserved role of HvNAC6 and ATAF1 in the regulation of penetration resistance in monocots and dicots, respectively.

Molecular cloning and characterization of two novel NAC genes from Mikania micrantha (Asteraceae)

“…Previous studies showed that plant NAC genes were implicated in responses to abiotic and biotic stimuli (e.g., Delessert et al, 2005;Jensen et al, 2007;Kim et al, 2007;Lin et al, 2007;Lu et al, 2007). Our analysis of the expression of MmATAF1 and MmNAP genes in shoots showed that they were also induced by mechanical wounding, ZnSO 4 , abscisic acid, and salicylic acid treatments with variable expression levels ( Figure 7B-E).…”

“…In recent years, a novel class of NAC proteins with a highly conserved NAC domain (for NAM, ATAF1/2, CUC2) (Aida et al, 1997) was identified. The proteins were recognized as transcription factors (Fujita et al, 2004;Tran et al, 2004) that participated in the formation of embryos (Duval et al, 2002), leaf senescence (Guo and Gan, 2006;Uauy et al, 2006), flower organ development (Sablowski and Meyerowitz, 1998), fruit development and senescence (Liu et al, 2009), cell cycle control (Kim et al, 2006), seed development , secondary-wall formation (Mitsuda et al, 2007;Mitsuda and Ohme-Takagi, 2008), hormone signaling (Fujita et al, 2004;Jensen et al, 2008), responses to pathogens and insect feeding (Delessert et al, 2005;Jensen et al, 2007;Lin et al, 2007), as well as responses to different abiotic stresses (Kim et al, 2007;Lu et al, 2007).…”

Dual function of Arabidopsis ATAF1 in abiotic and biotic stress responses

“…Additionally, NAC proteins have been implicated in disease defense and abiotic stress signaling. Several NAC proteins have been shown to interact with virus proteins [19][20][21], or to play direct roles in regulating pathogen defense [22]. Some NAC proteins were recently identified as abiotic stress regulators.…”

“…The ataf1-1 mutant line showed decreased resistance to a biotrophic fungus as a consequence of increased ABA level [22,31]. ATAF1 was also reported to be a negative regulator in drought response based on analysis of ataf1 mutants [32].…”

A structural view of the conserved domain of rice stress-responsive NAC1

“…Among the three members, after which this family is named, NAM (No Apical Meristem) from petunia is important for shoot apical meristem formation (Souer et al, 1996), CUC2 (cup-shaped cotyledon) is involved in controlling the formation of boundary cells of the meristem (Aida et al, 1997), and ATAF1, 2 show dual function in biotic and abiotic stress responses (Collinge and Boller, 2001;Delessert et al, 2005;Jensen et al, 2007;Lu et al, 2007;Jensen et al, 2008;Wang et al, 2009;Wu et al, 2009).…”