NAC transcription factors are one of the largest families of transcriptional regulators in plants, and members of the NAC gene family have been suggested to play important roles in the regulation of the transcriptional reprogramming associated with plant stress responses. A phylogenetic analysis of NAC genes, with a focus on rice and Arabidopsis, was performed. Herein, we present an overview of the regulation of the stress responsive NAC SNAC/(IX) group of genes that are implicated in the resistance to different stresses. SNAC factors have important roles for the control of biotic and abiotic stresses tolerance and that their overexpression can improve stress tolerance via biotechnological approaches. We also review the recent progress in elucidating the roles of NAC transcription factors in plant biotic and abiotic stresses. Modification of the expression pattern of transcription factor genes and/or changes in their activity contribute to the elaboration of various signaling pathways and regulatory networks. However, a single NAC gene often responds to several stress factors, and their protein products may participate in the regulation of several seemingly disparate processes as negative or positive regulators. Additionally, the NAC proteins function via auto-regulation or cross-regulation is extensively found among NAC genes. These observations assist in the understanding of the complex mechanisms of signaling and transcriptional reprogramming controlled by NAC proteins.

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Roles of NAC transcription factors in the regulation of biotic and abiotic stress responses in plants

Rice feeds more than half of the world's population. Rice blast, caused by the fungal pathogen Magnaporthe oryzae, and bacterial blight, caused by the bacterial pathogen Xanthomonas oryzae pv. oryzae, are major constraints to rice production worldwide. Genome sequencing and extensive molecular analysis has led to the identification of many new pathogen-associated molecular patterns (PAMPs) and avirulence and virulence effectors in both pathogens, as well as effector targets and receptors in the rice host. Characterization of these effectors, host targets, and resistance genes has provided new insight into innate immunity in plants. Some of the new findings, such as the binding activity of X. oryzae transcriptional activator–like (TAL) effectors to specific rice genomic sequences, are being used for the development of effective disease control methods and genome modification tools. This review summarizes the recent progress toward understanding the recognition and signaling events that govern rice innate i...

/pdf/novel-insights-into-rice-innate-immunity-against-bacterial-1ybjfj2udx.pdf

Novel insights into rice innate immunity against bacterial and fungal pathogens.

The NAC transcription factors play critical roles in regulating stress responses in plants. However, the functions for many of the NAC family members in rice are yet to be identified. In the present study, a novel stress-responsive rice NAC gene, ONAC022, was identified. Expression of ONAC022 was induced by drought, high salinity, and abscisic acid (ABA). The ONAC022 protein was found to bind specifically to a canonical NAC recognition cis-element sequence and showed transactivation activity at its C-terminus in yeast. The ONAC022 protein was localized to nucleus when transiently expressed in Nicotiana benthamiana. Three independent transgenic rice lines with overexpression of ONAC022 were generated and used to explore the function of ONAC022 in drought and salt stress tolerance. Under drought stress condition in greenhouse, soil-grown ONAC022-overexpressing (N22oe) transgenic rice plants showed an increased drought tolerance, leading to higher survival ratios and better growth than wild-type (WT) plants. When grown hydroponically in Hogland solution supplemented with 150 mM NaCl, the N22oe plants displayed an enhanced salt tolerance and accumulated less Na(+) in roots and shoots as compared to WT plants. Under drought stress condition, the N22oe plants exhibited decreased rates of water loss and transpiration, reduced percentage of open stomata and increased contents of proline and soluble sugars. However, the N22oe lines showed increased sensitivity to exogenous ABA at seed germination and seedling growth stages but contained higher level of endogenous ABA. Expression of some ABA biosynthetic genes (OsNCEDs and OsPSY), signaling and regulatory genes (OsPP2C02, OsPP2C49, OsPP2C68, OsbZIP23, OsAP37, OsDREB2a, and OsMYB2), and late stress-responsive genes (OsRAB21, OsLEA3, and OsP5CS1) was upregulated in N22oe plants. Our data demonstrate that ONAC022 functions as a stress-responsive NAC with transcriptional activator activity and plays a positive role in drought and salt stress tolerance through modulating an ABA-mediated pathway.

/pdf/overexpression-of-a-stress-responsive-nac-transcription-50yg4ylgtf.pdf

Overexpression of a Stress-Responsive NAC Transcription Factor Gene ONAC022 Improves Drought and Salt Tolerance in Rice

NAC (NAM, ATAF, and CUC) transcription factors play important roles in plant biological processes, including phytohormone homeostasis, plant development, and in responses to various environmental stresses. TaNAC29 was introduced into Arabidopsis using the Agrobacterium tumefaciens-mediated floral dipping method. TaNAC29-overexpression plants were subjected to salt and drought stresses for examining gene functions. To investigate tolerant mechanisms involved in the salt and drought responses, expression of related marker genes analyses were conducted, and related physiological indices were also measured. Expressions of genes were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR). A novel NAC transcription factor gene, designated TaNAC29, was isolated from bread wheat (Triticum aestivum). Sequence alignment suggested that TaNAC29 might be located on chromosome 2BS. TaNAC29 was localized to the nucleus in wheat protoplasts, and proved to have transcriptional activation activities in yeast. TaNAC29 was expressed at a higher level in the leaves, and expression levels were much higher in senescent leaves, indicating that TaNAC29 might be involved in the senescence process. TaNAC29 transcripts were increased following treatments with salt, PEG6000, H2O2, and abscisic acid (ABA). To examine TaNAC29 function, transgenic Arabidopsis plants overexpressing TaNAC29 were generated. Germination and root length assays of transgenic plants demonstrated that TaNAC29 overexpression plants had enhanced tolerances to high salinity and dehydration, and exhibited an ABA-hypersensitive response. When grown in the greenhouse, TaNAC29-overexpression plants showed the same tolerance response to salt and drought stresses at both the vegetative and reproductive period, and had delayed bolting and flowering in the reproductive period. Moreover, TaNAC29 overexpression plants accumulated lesser malondialdehyde (MDA), H2O2, while had higher superoxide dismutase (SOD) and catalase (CAT) activities under high salinity and/or dehydration stress. Our results demonstrate that TaNAC29 plays important roles in the senescence process and response to salt and drought stresses. ABA signal pathway and antioxidant enzyme systems are involved in TaNAC29-mediated stress tolerance mechanisms.

https://link.springer.com/content/pdf/10.1186%2Fs12870-015-0644-9.pdf

TaNAC29, a NAC transcription factor from wheat, enhances salt and drought tolerance in transgenic Arabidopsis

Abiotic and biotic stresses adversely affect the growth and productivity of plants and constitute the major yield-limiting factor in agriculture. In recent years, several  transcription factors (TF) have been identified that can function as switches to control the expression of potential stress-related genes. These transcription factors play crucial roles in governing transcriptional reprogramming during development in plant biological systems and are also capable of increasing the tolerance of plants to abiotic and biotic stresses. Thus, identifying and characterizing critical genes that are involved in plant stress responses are essential for the development of transgenic plants that exhibit enhanced stress tolerance. This review describes the DREB/ERF, MYB, NAC and WRKY TF and summarizes the studies that highlight their potential in engineering abiotic and biotic stress tolerance in transgenic plants.

Potential use of the DREB/ERF, MYB, NAC and WRKY transcription factors to improve abiotic and biotic stress in transgenic plants

NAC (NAM/ATAF/CUC) transcription factors have important functions in regulating plant growth, development, and abiotic and biotic stress responses. Here, we characterized two rice pathogen-responsive NAC transcription factors, ONAC122 and ONAC131. We determined that these proteins localized to the nucleus when expressed ectopically and had transcriptional activation activities. ONAC122 and ONAC131 expression was induced after infection by Magnaporthe grisea, the causal agent of rice blast disease, and the M. grisea-induced expression of both genes was faster and higher in the incompatible interaction compared with the compatible interaction during early stages of infection. ONAC122 and ONAC131 were also induced by treatment with salicylic acid, methyl jasmonate or 1-aminocyclopropane-1-carboxylic acid (a precursor of ethylene). Silencing ONAC122 or ONAC131 expression using a newly modified Brome mosaic virus (BMV)-based silencing vector resulted in an enhanced susceptibility to M. grisea. Furthermore, expression levels of several other defense- and signaling-related genes (i.e. OsLOX, OsPR1a, OsWRKY45 and OsNH1) were down-regulated in plants silenced for ONAC122 or ONAC131 expression via the BMV-based silencing system. Our results suggest that both ONAC122 and ONAC131 have important roles in rice disease resistance responses through the regulated expression of other defense- and signaling-related genes.

Xueping Zhou

Papers

Functions of rice NAC transcriptional factors, ONAC122 and ONAC131, in defense responses against Magnaporthe grisea