Functional Characterization Of Rice NAC Transcription Factors ONAC131, MNAC1 And ONAC095 In Resistance To Abiotic And Biotic Stresses

Rice will suffer a lot of adverse stresses in the growth stage, and the stresses would result in the yield loss in some extreme cases. In the interaction with these stresses, rice has formed a set of adaption mechanism. Transcription factors, as important regulatory genes, play important roles in the resistance to adverse stresses. NAC transcription factors, as one of the largest plant specific family genes, are involved in plant growth and development as well as the resistance to adverse stresses. In this paper, we have focused on the functional characterization of three NAC transcription factors ONAC131, MNAC1 and ONAC095.ONAC131 is one member of the SNAC group, which is related to stress resistance. Using the GUS stain method, the ONAC131 promoter transgenic lines could be only stained in episperm, ligule and sheath. The ONAC131 has transactivational activity, and the activation domain locates in the C terminal, and serial truncation of the C terminal proves that the 228-243aa at C terminal is indispensible for the transactivational activity. Chimeric repression of ONAC131 has enhaced the tolerance to Xanthomonas oryzae pv. Oryzae and the amount of bacteria is significantly reduced in the ONAC131 SRDX lines, the expression of disease related genes such as PAL、 PR10、Jamyb is also significantly reduced in the ONAC131 SRDX lines. Chimeric repression of ONAC131 could reduce resistance to salt, drought and cold stresses, the expression of cold related gene (CDPK7, SRO1c, SODB, OsTrx23, Lti6a, Lti6b, GSTU6 and Peroxidase16) is also significantly reduced in the ONAC131 SRDX Lines.According to the chip data and experiment verification, we have identified four NAC genes which could be highly induced by Magnaporthe grisea and named them as MNACs (M. grisea induced NACs). The four MNACs (MNAC1-4) all locate in nucleus and poss transactivational activity. The transcription activation domain of MNAC1 is located in the C terminal and serial truncation proves that the 246-276aa at C terminal is indispensible for the transactivational activity. We have emphasized the function characterization of MNAC1. Over-expression MNAC1 has enhanced the susceptibility to M.grisea and the lesion size and amount of fungal are both significantly larger than the wild type after four days of M.grisea inoculation; the disease related genes such as PR1a, PR3, PR4, PR8, PR10, PAL, PAD4, CHS, etc all show significantly reduced expression before and after M.grisea inoculation; the SA and JA content of MNAC1 over-expression lines are also significantly reduced compared with the wild type after M. grisea inoculation.ONAC095 could be induced by lots of abiotic stresses as well as ABA treatment. ONAC095 locates in the nucleus and posses transactivational activity. The activation domain locates in the 242-258aa sequences of C terminal and the prolines at 246, 252aa were indispensible for the activation activity. Using rice transformation, we have obtained ONAC095 over-expression and chimeric repression lines.The ONAC095 chimeric repression lines have enhanced tolerance to drought stress and the proline and soluble sugar content are also significantly higher than the wild type after drought treatment. The expression of drought related genes (RAB21, AP37, RAB16D, bZIP23, PP2C68 and ERD1) is also significantly higher than the wild type after drought treatment. The ONAC095 chimeric repression lines have also enhanced sensitivity to ABA and accumulated more ABA content compared with the wild type. The expression of ABA metabolism gene (ABA8OX3) and ABA synthesis ABA signal related genes (NCED4, NCED5, PP2C30 and PP2C49) is significantly lower and higher, respectively, compared with the wild type. In the cold treatment, ONAC095 chimeric repression lines have accumulated more superoxide anion and H2O2.The ROS related enzymes (SOD and CAT) activities are also significantly lower before and after cold treatment compared with the wild type.The expression of H2O2 synthesis genes (RbohA, RbohB, RbohD, RbohG and RbohH) is significantly higher than the wild type after cold treatment compared with wild type, whereas the expression of cold related genes (WRKY76, CDPK7, RAN1, ICE and TRX23) is significantly lower than the wild type after cold treatment compared with wild type. We speculated the enhaced tolerance to drought was dependent on ABA and the reduced tolerance to cold was due to accumulation of more superoxide anion and H2O2.