Os11g0184900

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The OsNAC5 gene is a member of plant specific NAC family in rice that encodes a transcript factor to regulate stress responses.

Annotated Information

Function

Stress-responsive proteins OsNAC5 is a transcriptional activator induced by abiotic stress,including drought,cold and high salinity.By microarray analysis,OsNAC5 upregulates many stress-inducible genes,including OsLEA3( the late embryogenesis abundant gene) and Os06g0681200 in rice plant that overexpressed OsNAC5.By gel mobility shift assay demonstrated that this protein bind specifically to the NAC recognition sequence of the OsLEA3 promoter (-56 to -85) and enhance the expression of this stress-related gene. Moreover,OsNAC5-overexpressing plants did not retard growth under non-stressed conditions. Hence, OsNAC5 may be an effective gene to enhance the stress tolerance of rice without inviting growth defects [1]. In addition to abiotic stress, expression of OsNAC5 was also responsive to ABA,MeJA and other plant hormones such as ethylene,IAA,SA and BR could also induce rapid upregulation of OsNAC5 [2][3].

Fig.1 Expression of OsNAC3, OsNAC4,OsNAC5, OsNAC6 and SNAC1 in response to dehydration, cold temperature(4°C), high salinity, and ABA or MeJA in rice plants(From reference [1]).

OsNAC5 has been characterized as a novel senescence associated ABA-dependent NAC transcription factor [3]. The promoter regions of OsNAC5 which contain a conserved ABRE sequences (ACGTG G/TC) are activated in response to ABA [1]. It is possible that OsNAC5 protein regulates similar transporter genes in rice and that these genes are needed for effective Fe and Zn remobilization [4].

OsNAC5 involves in modulating several downstream functional genes (associated with accumulation of compatible solutes,Na+,H2O2 and malondialdehyde. By detecting some metabolic changes,such as greater amounts of Pro and soluble sugars, and less amounts of MDA and H2O2 accumulated in OsNAC5-overexpressing rice plants suggests that it can protect plants from dehydration and oxidative damage in response to abiotic stresses [2].

OsNAC5 is a metal homeostasis related gene. Final seed Fe, Zn and protein concentrations were positively correlated with high and early OsNAC5 expression level in flag leaves (the major source of remobilized metals for developing seeds)during panicle emergence stage.(Sperotto et al., 2009)[3].The increase expression of OsNAC5 in NH+4 (compared with NH4+:NO3-) demonstrates that the NAC domain is crucial to plant development [5].

Mutation

Fig.2 WT, OE1, Ri5 and Ri6 rice seedlings treated with cold (4°C for 6 days),salt stress(200 mM NaCl for 14 days),drought(withholding of water for 15 days).(From reference [2]).

The knockdown lines (Ri5, Ri6) less tolerant to cold,drought and salt stress, while overexpression of OsNAC5 (OE1) rice seedings conferred greater tolerance to these abiotic stress (Fig.2)[2].

Under the control of the root-specific (RCc3) and constitutive (GOS2) promoters,the overexpressed OsNAC5 could improve rice plant tolerance to drought and high salinity during the vegetative stage of growth. Moreover,Root-specific overexpression of OsNAC5 can significantly enlarge the root diameter in transgenic rice plants via enlarging steles and aerenchymas at the reproductive stage of growth(Fig.6)[6]. It suggests the importance of this phenotype to improve grain yield.(Fig.3) [6].

Fig.6 Light microscopic images of cross-sectioned RCc3:OsNAC5, GOS2:OsNAC5 and NT roots (10 cm down from the ground surface level)during the panicle heading stage. The position of the metaxylem vessel (Me) and aerenchyma (Ae) are indicated. Scale bars, 500 lm in the upper panels and 100 lm in the lower panels.(From reference [6]).
Fig.3 Drought stress tolerance of RCc3:OsNAC5 and GOS2:OsNAC5 plants.(From reference [6]).

Expression

Each OsNAC gene has a unique expression pattern. OsNAC5 is predominantly expressed in root and embryo [7].
Fig.4 Expression patterns of OsNAC5 in different.(From reference [2]).

Surprisingly,later studies found that it expresses in leaves, roots, stems and flowers(Fig.2) and higher expression in flag leaves, non-flag leaves panicles and Lower expression in stems and roots, with no detectable expression in leaf blades of mature plants and young panicles(Fig.7). A possible explanation for such differences in organ specificity could be the use of a different cultivar and of a completely different experiment strategy for transcript detection [2][3].

Fig.7 Relative expression levels (qRT-PCR, relative to Ubiquitin expression) of OsNAC5 in different rice organs collected during the grain filling stage.(From reference [3]).
Primer Forward primer Reverse primer
Gene amplication 5′-CGCGGATCCATGGAGTGCGGTGGTGCGCTG-3′; 5′-CGGGGTACCTTAGAACGGCTTCTGCAGGTAC-3′;([2])
RT-PCR 5′-ATGGAGTGCGGTGGTGCGCT-3′ 5′-TTAGAACGGCTTCTGCAGGT-3′ [6]
5′-TTCAAGAACA-CATCCCTG-3′ 5′-GAAGTGAACTGAAGTACC-3′ [7]

Evolution

Fig.5 A dendrogram of NAC genes based on the amino-acid sequences of their NAC domains(The tree was made by the neighbor-joining method).(From reference [7]).

Amino acid sequence analysis revealed that the NAC genes in plants can fall into several subfamilies, such as the NAM, ATAF, and OsNAC3 subfamilies.OsNAC5 and OsNAC6 represent ATAF subfamily in rice [7].

According to phylogenetic relationship, NAC family with 151 members in rice is divided into five groups. OsNAC5 belongs to the third subgroup with SNAC1 and OsNAC6/SNAC2 [8] [9].

Knowledge Extension

Subcellular localization studies using OsNAC5-GFP fusion proteins showed that OsNAC5 is localized to the nucleus.Transactivation assays demonstrated that OsNAC5 is a transcriptional activator that its activation domain lies C-terminal region between aa 273 and 328 [1].

By yeast two-hybrid screening and pull-down assays in vitro demonstrated that OsNAC5 interacts with other OsNACs including itself to form homodimers and heterodimers. It also suggested that NAC-domain plays complex roles in binding to DNA and proteins[10].

Like others members of the NAM-ATAF-CUC (NAC) protein family，OsNAC5 contains a highly conserved N-terminal NAC-domain and a variable C-terminal domain.C-terminal region comprising the acidic, proline-, and serine-rich elements are responsible for transcriptional activation [10].

Labs working on this gene

  • School of Biotechnology and Environmental Engineering, Myongji University, Yongin, 449-728, South Korea
  • Laboratory of Plant Molecular Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo, 1138657, Japan
  • Centro de Biotecnologia, Universidade Federal do Rio Grande do Sul, P.O. Box 15005, 91501-970, Porto Alegre, RS, Brazil
  • State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, The Chinese Academy of Sciences, Beijing, 100093, People’s Republic of China
  • Laboratory of Plant Breeding and Genetics, Graduate School of Agricultural and Life Sciences, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan

References

  1. ↑ 1.0 1.1 1.2 1.3 Takasaki H., Maruyama K., Kidokoro S., Ito Y., Fujita Y., et al. (2010) The abiotic stress-responsive NAC-type transcription factor OsNAC5 regulates stress-inducible genes and stress tolerance in rice. Mol Genet Genomics 284: 173–183.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Song, S.Y., Chen, Y., Chen, J., Dai, X.Y. and Zhang, W.H. (2011) Physiological mechanisms underlying OsNAC5-dependent tolerance of rice plants to abiotic stress. Planta 234: 331–345.
  3. ↑ 3.0 3.1 3.2 3.3 Sperotto RA, Ricachenevsky FK, Duarte GL, BoV T, Lopes KL, et al. (2009) Identification of up-regulated genes in flag leaves during rice grain filling and characterization of OsNAC5, a new ABA-dependent transcription factor. Planta 230: 985–1002.
  4. ↑ Raul A. Sperotto, Tatiana Boff, Guilherme L. Duarte, Lívia S. Santos,Michael A. Grusakc, et al. (2010) Identification of putative target genes to manipulate Fe and Zn concentrations in rice grains. Journal of Plant Physiology 167: 1500–1506.
  5. ↑ Marta S. Lopes and Jose L. Araus (2008) Comparative genomic and physiological analysis of nutrient response to NH4+, NH4+: NO3- and NO3- in barley seedlings. Physiologia Plantarum 134: 134–150.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Jeong, J. S., Kim,Y. S., Redillas, M. C. F. R., Jang, G., Jung, H., Bang, S. W.,et al. (2013) OsNAC5 overexpression enlarges root diameter in rice plants leading to enhanced drought tolerance and increased grain yield in the field. Plant Biotechnology Journal, 11: 101–114.
  7. ↑ 7.0 7.1 7.2 7.3 Kikuchi K, Ueguchi-Tanaka M, Yoshida KT, Nagato Y, Matsusoka M, et al. (2000) Molecular analysis of the NAC gene family in rice. Mol Gen Genet 262: 1047–1051.
  8. ↑ Fang YJ, You J, Xie KB, Xie WB, Xiong LZ (2008) Systematic sequence analysis and identification of tissue-specific or stressresponsive genes of NAC transcription factor family in rice. MolGenet Genomics 280: 547–563.
  9. ↑ Nuruzzaman M, Manimekalai R, Sharoni AM, Satoh K, Kondoh H,et al. (2010) Genome-wide analysis of NAC transcription factor family in rice. Gene 465: 30–44.
  10. ↑ 10.0 10.1 Jeong, J.S., Park, Y.T., Jung, H., Park, S.H. and Kim, J.-K. (2009) Rice NAC proteins act as homodimers and heterodimers. Plant Biotechnol. Rep 3: 127–134.

Structured Information

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