A similar response was observed for JcNAC1 from Jatropha curcas, a woody plant
used for biodiesel production, whose overexpression produced plants with enhanced
tolerance to drought and increased susceptibility to pathogens (Qin et al. 2014).
OsNAC6 and OsNAC5 increased high-salinity and drought tolerance, and the overexpression of OsNAC10 produced rice plants with enhanced drought tolerance at the
reproductive stage and increased the grain yield by 25–42% under drought conditions
(Jin and Kim 2010). Several NAC proteins from Brassica napus were upregulated
in response to biotic and abiotic stresses, including wounding, insect feeding, cold
shock, pathogen infection and drought stress (Hegedus et al. 2003; Niu et al. 2014; Liu
et al. 2015), and, interestingly, the overexpression of BnNAC2 and BnNAC5 genes
in yeast enhanced the cells’ sensitivity to high-salinity and osmotic stresses (Zhong
et al. 2012).
In Norway spruce, orthologs of these stress-characterized Arabidopsis genes have
been identified in transcriptome studies in response to biotic stress (Danielsson et al.
2011; Lunden et al. 2015), indicating that a regulatory network involved in plant
responses to stress could be conserved between angiosperms and gymnosperms,
despite their evolutionary divergence. Recently, it has been shown that PaNAC03 is
responsive to biotic stress and may be implicated in the control of defence-associated
secondary metabolite production. Its overexpression produced aberrant embryos and
several genes involved in flavonoid pathways such as chalcone synthase (CHS),
flavonoid-3
0 -hydroxylase (F3
0 H ) and leucoanthocyanidin reductase 3 (PaLAR3)
were misregulated. These lines also showed reduced levels of specific flavonoids
(Dalman et al. 2017).
The characterization of CsNAN1 in Citrus reshni also showed an extensive similarity in its action mode with ANAC019, ANAC055 and ANAC072 from Arabidopsis
and was strongly induced by drought stress, salt, cold and ABA (de Oliveira et al. 2011).
In addition, these TFs have been demonstrated to have a key function in the tolerance of some woody plants to unfavourable environmental conditions. In Populus
euphratica, a woody plant that grows in dry deserts and maintains high growth and
photosynthetic rates at high salinity, the expression of PeNAC1 is increased by salt and
drought stress, and its overexpression in Arabidopsis enhances tolerance to salt stress
(Wang et al. 2013a). Similar results were observed in the woody plants Paulownia
tomentosa for several NAC TFs (Zhao et al. 2017) and Tamarix hispida for the
ThNAC13 TF (Wang et al. 2014). Transgenic plants overexpressing this TF had a
higher activity of antioxidant enzymes, such as superoxide dismutase (SOD) and
peroxidase (POD), and reduced reactive oxygen species levels compared to control
plants under salt or osmotic stress. The presence of NACRS elements in the promoters of SOD and POD suggests that ThNAC13 might improve tolerance by
regulating the transcription levels of these enzymes (Wang et al. 2017).
In a recent study, Chen et al. (2017) showed a significantly high expression level
of NAC genes after abscisic acid (ABA) treatment in Populus hopeiensis, a poplar
with high drought and cold tolerance (Wang et al. 2014). This plant hormone plays
an essential role in mediating the adaptation to stress and regulates root growth
(McAdam et al. 2016). In another woody plant species that is extremely cold-hardy
and drought resistant, Pyrus betulifolia, the overexpression of a NAC gene, PbeNAC1,
NAC Transcription Factors in Woody Plants
207
used for biodiesel production, whose overexpression produced plants with enhanced
tolerance to drought and increased susceptibility to pathogens (Qin et al. 2014).
OsNAC6 and OsNAC5 increased high-salinity and drought tolerance, and the overexpression of OsNAC10 produced rice plants with enhanced drought tolerance at the
reproductive stage and increased the grain yield by 25–42% under drought conditions
(Jin and Kim 2010). Several NAC proteins from Brassica napus were upregulated
in response to biotic and abiotic stresses, including wounding, insect feeding, cold
shock, pathogen infection and drought stress (Hegedus et al. 2003; Niu et al. 2014; Liu
et al. 2015), and, interestingly, the overexpression of BnNAC2 and BnNAC5 genes
in yeast enhanced the cells’ sensitivity to high-salinity and osmotic stresses (Zhong
et al. 2012).
In Norway spruce, orthologs of these stress-characterized Arabidopsis genes have
been identified in transcriptome studies in response to biotic stress (Danielsson et al.
2011; Lunden et al. 2015), indicating that a regulatory network involved in plant
responses to stress could be conserved between angiosperms and gymnosperms,
despite their evolutionary divergence. Recently, it has been shown that PaNAC03 is
responsive to biotic stress and may be implicated in the control of defence-associated
secondary metabolite production. Its overexpression produced aberrant embryos and
several genes involved in flavonoid pathways such as chalcone synthase (CHS),
flavonoid-3
0 -hydroxylase (F3
0 H ) and leucoanthocyanidin reductase 3 (PaLAR3)
were misregulated. These lines also showed reduced levels of specific flavonoids
(Dalman et al. 2017).
The characterization of CsNAN1 in Citrus reshni also showed an extensive similarity in its action mode with ANAC019, ANAC055 and ANAC072 from Arabidopsis
and was strongly induced by drought stress, salt, cold and ABA (de Oliveira et al. 2011).
In addition, these TFs have been demonstrated to have a key function in the tolerance of some woody plants to unfavourable environmental conditions. In Populus
euphratica, a woody plant that grows in dry deserts and maintains high growth and
photosynthetic rates at high salinity, the expression of PeNAC1 is increased by salt and
drought stress, and its overexpression in Arabidopsis enhances tolerance to salt stress
(Wang et al. 2013a). Similar results were observed in the woody plants Paulownia
tomentosa for several NAC TFs (Zhao et al. 2017) and Tamarix hispida for the
ThNAC13 TF (Wang et al. 2014). Transgenic plants overexpressing this TF had a
higher activity of antioxidant enzymes, such as superoxide dismutase (SOD) and
peroxidase (POD), and reduced reactive oxygen species levels compared to control
plants under salt or osmotic stress. The presence of NACRS elements in the promoters of SOD and POD suggests that ThNAC13 might improve tolerance by
regulating the transcription levels of these enzymes (Wang et al. 2017).
In a recent study, Chen et al. (2017) showed a significantly high expression level
of NAC genes after abscisic acid (ABA) treatment in Populus hopeiensis, a poplar
with high drought and cold tolerance (Wang et al. 2014). This plant hormone plays
an essential role in mediating the adaptation to stress and regulates root growth
(McAdam et al. 2016). In another woody plant species that is extremely cold-hardy
and drought resistant, Pyrus betulifolia, the overexpression of a NAC gene, PbeNAC1,
NAC Transcription Factors in Woody Plants
207