| Plants are subjected to various types of abiotic (e.g. high-salinity, drought, and cold) and biotic (e.g. pathogen infection, insect fedding, and parasitic plants) stresses in their growth and development environments. To survive under such environment, plants have developed a series of mechanisms at physiological, biochemical, and molecular levels to adapt and defend themselves against these stresses. During these processes, different types of transcription factors play critical roles in plant defense response to biotic and abiotic stresses through directly or indirectly regulation of stress-related genes. NAC (NAM/ATAF/CUC) transcription factor, as one of largest and plant-specific gene families exsists in many different plants. The common characteristics of the NAC protein are the presence of a conserved NAC domain, composing of about150amino acids in N-terminals, and a highly variable transcriptional activation region in C-terminals. Extensive studies have revealed that NAC transcription factors not only play important roles in plant growth and development, but also have functions in regulation of responses to biotic and abiotic stresses. The study systematically investigated the expression characterization of ONAC genes under the different biotic and abiotic stresses. Based on the overlapping expression characteization, we isolated21ONAC genes from rice and investigated the expression patterns of these21ON AC genes after pathogens infection, and exogenous hormones salicylic acid (SA), methyl jasmonate (MeJA), ACC (ethylene,ET). The molecular characterization and the function of some ONAC genes were also investigated in this study. All of these studies will provide potential utility in rice genetic improvement of stress resistacne in rice.The major results of ONAC genes in this study were showed in the following aspects:Microarray data analyses revealed that about63ONAC genes were overlapping expression during in various abiotic (salinity, drought, and Cold) and biotic stress (Magnaporthe grisea, Striga hermonthica, Xoo, Xoc, and RSV) conditions. Most of ONAC genes were up-regulated expression response to salt, dry, cold, Magnaporthe grisea, Striga hermonthica,and RSV. For the abotic stresses.38genes were overlapping expression in any two stress conditions.16among30representative ONAC genes were up-regulated expression response to Abscisic acid (ABA). For the biotic stresses,65ONAC genes were overlapping expression in any two biotic stresses. The phylogenetic tree suggested that these ONAC genes were classified into10subgroups [OsNAC7(SND), ONAC11(NAC1), SNACâ… , SNACâ…¡ (NAM/CUC3), SNACâ…¢ (TIP), SNACâ…£ (ANAC34), ONAC079(ONAC6), ONAC012(ONAC7), ONAC135(ONAC3). ONAC100(ONAC2)]. Homology sequence search found that there were many highly ortholgous genes in ONAC genes family. The overlapping expression of ONAC genes indicated that ONAC genes might play important roles in the cross-talk of different abiotic and biotic stresses and might have the multiple biological functions for the stress conditions.We isolated21ONAC genes from rice and investigated the expression patterns of these21ONAC genes after pathogens infection, and exogenous hormones SA, MeJA, ACC. For pathogens infection, two interaction systems of rice-Magnaporthe grisea and rice-Xanthomonas oryzae pv.oryzae (Xoo) were used. The results showed that most of them were induced by the SA, JA and ACC (ET) except ONAC066and ONAC058. Among these,12ONAC genes(OsNAC8,ONAC016,ONAC022,ONAC023,ONAC049, ONAC054,ONAC061,ONAC063,ONAC075,ONAC095,ONAC122,and ONAC131) were strongly induced by ACC(ET),6ONAC genes (SNAC1,OsNAC4,OsNAC5,OsNAC6, ONAC103, and ONAC121) were strongly induced by JA. The expression patterns of21isolated ONAC genes in incompatible and compatible combinations between rice and Magnaporthe grisea, rice and Xoo were analyzed. The results showed that11ONAC genes (ONAC022, ONAC023, ONAC049, ONAC054, ONAC061, ONAC075, ONAC095, ONAC103, ONAC121, ONAC122, and ONAC131) were more strongly induced in the incompatible interaction than compatible interaction in these two combinations. According to the expression patterns, these11ONAC genes may be involved in resistance to fungal blast disease and bacterial blight of rice. In addition,3ONAC genes (OsNAC6, OsNAC8, and ONAC063) may be involved in resistance to fungal blast disease and susceptivity to Bacterial blight of rice, and4ONAC genes (OsNAC3, OsNAC4, ONAC016, and ONAC058) may be involved in resistance to Bacterial blight of rice. Transient expression in tobacco epidermal cells indicated that ONAC-GFP fusion proteins including ONAC023, ONAC063, ONAC095, ONAC122, and ONAC131were localized in the nucleus. Transactivation analysis showed that ONAC023, ONAC063. ONAC095, ONAC122, or ONAC131played as a role in the activator of transcription.We investigated the function of some ONAC genes in rice through virus-induced gene silencing (VIGS). The results showed that some pathogen relative genes (Oseds1, OsPAD4, OsLOX, OsPR3, OsPR1a, OsWRKY45, OsJamyb, and OsNHl/NPR1) were downregulation when ONAC023,ONAC095, ONAC122, ONAC131, or OsNAC6was silenced respectively, and finally the rice became more susceptive to rice blast.These results indicated that ONAC023, ONAC095, ONAC122, ONAC131, and OsNAC6were related to the resistance to rice blast disease. In addition, the rice seedling became more susceptive to rice bacterial blight when ONAC023or ONAC095was silenced respectively, which indicated that ONAC023and ONAC095play the positive roles in resistance to rice bacterial blitht.To study the function of ONAC genes in disease resistance and stress tolerance, we constructed overexpression vectors (ONAC-OE) and chimeric repressor vectors (ONAC-SRDX) of isolated ONAC genes, and introduced them into wild-type rice XiuShui-11. In the present study, we have obtained some transgenic lines of ONAC genes and To seeds of ONAC075-oe, OsNAC6-oe transgenic lines. Furthermore, the function analysis of ONAC075-oe, OsNAC6-oe transgenic lines showed that ONAC075-oe and OsNAC6-oe can improve the blast disease resistance and drought stress tolerance. |
