Os03g0815100

SNAC1 (STRESS-RESPONSIVE NAC 1) is a member of rice stress-responsive NAC family in rice.

Annotated Information

Function

• The transgenic rice also shows significantly improved drought resistance and salt tolerance at the vegetative stage. SNAC1 is induced predominantly in guard cells by drought and encodes a NAM, ATAF, and CUC(NAC) transcription factor with transactivation activity. DNA chip analysis revealed that a large number of stress-related genes were up-regulated in the SNAC1 overexpressing rice plants. Thus, SNAC1 holds promising utility in improving drought and salinity tolerance in rice. This gene may show great promise for the genetic improvement of stress tolerance in cotton.

• The SNAC1 NAC domain:
  • The structure of the SNAC1 NAC domain shares a similarity with a transcription factor fold identified by ANAC NAC domain, and consists of a central semi-β-barrel formed by seven twisted anti-parallel β-strands with three α-helices on one side and the open side respectively.
  • This domain mediates dimerization of the NAC proteins through conserved interactions and indicates that the dimerization should be conserved in NAC family. Moreover, stabilization of the loop region between β1 and 2 by Arg88 is hypothesized to be responsibile for DNA binding.

Genes related to SNAC1

• Target gene of SNAC1:
  • OsSRO1c, was identified as a direct target gene of SNAC1 involved in the regulation of stomatal aperture and oxidative response.
  • SNAC1 could bind to the promoter of OsSRO1c and activate the expression of OsSRO1c. OsSRO1c has dual roles in drought and oxidative stress tolerance of rice by promoting stomatal closure and H₂O₂ accumulation through a novel pathway involving regulators SNAC1 and DST.
• Gene regulated by SNAC1:
  • Some Stress Related Genes:
    • SNAC1 encodes a NAC transcription factor that regulates many stress related genes,such as DREB1A, CBF, SCOF, Tsi, and OSISAP1.
  • OsPP18:
    • OsPP18 is a novel PP2C gene which is regulated by SNAC1 and confers drought and oxidative stress tolerance by regulating ROS homeostasis through ABA-independent pathways.
    • SNAC1 can bind to the promoter of the OsPP18 gene and activates its expression.

GO assignment(s): GO:0003677, GO:0045449

Mutation

• seven independent positive transgenic plants:
  • S8
  • S19
  • S21
  • S24
  • S25
  • S18
  • S23
  • The five(S8, S19, S21, S24, and S25) plants had high levels of transgene expression whereas the other two(S18 and S23) had no expression of transgene. S18 was thus used as a negative control for further analysis. Southern blot analysis. Southern blot analysis suggested that all of the five expression-positive plants had 1–2 copies of T-DNA .
  • All of the SNAC1-overexpressing plants produced significantly higher spikelet fertility than the negative control under all three treatments. Under severe drought stress in which the WT and the negative control produced almost no seeds, the five transgenic lines had 23.0–34.6% spikelet fertility. While the moderate drought stress was conducted in the drought-prone field, SNAC1-overexpressing plants exhibited 17.4–22.3% higher spikelet fertility than theWT or the negative transgenic line S18. Under the stress conditions created using the PVC pipes, the transgenic lines showed 17.2–24.0% higher seed setting than the control. Under well irrigated conditions, all transgenic and control plants had similar performance for spikelet fertility.
  • Compared with WT, the transgenic rice are more sensitive to abscisic acid and lose water more slowly by closing more stomatal pores, yet display no significant difference in the rate of photosynthesis.
• Transgenic plants:
  • S-1(SNAC1 transgenic line-1)
  • S-2(SNAC1 transgenic line-2)
  • S-3(SNAC1 transgenic line-3)
  • S-4(SNAC1 transgenic line-4)
  • S-5(SNAC1 transgenic line-5)
  • Southern blot showed three transgenic lines that appeared to contain a single-copy insertion, and they were identified as S-1, S-4 and S-5. Transgenic lines S-2 and S-3 had been proved as positive transgenic plants through PCR analysis, but did not show hybridization signals in southern blotting analysis. Northern blotting showed that mRNA transcription level of SNAC1 was diverse among the five transgenic lines. Two independent lines, S-1 and S-4, with high expression level of SNAC1, were selected and used for drought and salt-tolerance analysis.

Expression

• The SNAC1 gene is induced by drought predominantly in guard cells, and the GFP signal was observed for guard cells on both the upper and lower sides of leaves. Northern blot analysis revealed that the expression of this gene could be induced by drought, salt, cold, and abscisic acid.

• SNAC1-Overexpressing transgenic plants significantly improve drought resistance and salt tolerance at vegetative stage. Increased stomatal closure and ABA sensitivity may provide partial explanation for the observed drought resistance.

Evolution

• SNAC1 showed 98.6% sequence identity and the same location in the rice genome to the predicted gene ONAC044.
• In rice, most of the SNAC-A subgroup genes respond to JA. Among them, SNAC1, OsNAC3, and OsNAC4 are present in the same phylogenetic group.

Knowledge Extension

Figure 1. A model of a transcriptional cascade of OsNACs under abiotic stress condition in rice(from reference ).

• The rice stress-responsive NAC family includes five members: OsNAC3, OsNAC4, OsNAC5, OsNAC6, and SNAC1. Their expression was induced by abiotic stresses such as drought and high salinity. OsNAC5 and OsNAC6 are strongly induced by ABA and SNAC1 is also transiently induced by ABA. Three ABA-responsive elements (ABREs; ACGTG G/TC; red bars) exist in the OsNAC5 and OsNAC6 promoters. All of these genes are induced by JA and JA may mediate both abiotic and biotic stress signaling. Unknown factorsmaymediate abiotic stress signaling as shown with the dashed arrows. Overexpression of OsNAC5, OsNAC6, and SNAC1 are capable of enhancing stress tolerance. Although OsNAC5 is suggested to be a senescence-associated TF, the functions of the other OsNACs in relation to senescence are not well characterized.

• Some NAC genes outside of the SNAC group also show response to abiotic stress in rice. The rice ONAC045 gene in the NAC group NAM/CUC3 was induced by drought, high-salt, low temperature stress and in response to ABA treatment.

Figure 2.A model representing the regulation of NAC TFs at different levels during stress.(from reference ).

• The complex post-transcriptional regulation involves micro-RNA (miRNA)-mediated cleavage of genes (Figure 2).NAC TFs also undergo intensive post-translational regulation which includes protein degradation mediated by ubiquitins, dimerization and interaction with other non-NAC proteins.Upon translation, such DREB-type and AREB-type proteins could counter-control the transcription of NAC genes. Furthermore, expression of stress-responsive NACs may be tightly regulated by several stress-responsive cis-acting elements contained in the promoter region(Figure 2).

• NAC family, which is one of the largest plant transcription factor families, is only found in plants to date. Proteins of this family are characterized by a highly conserved DNA binding domain, known as NAC domain in the N-terminal region. In contrast, the C-terminal region of NAC proteins, usually containing the transcriptional activation domain, is highly diversified both in length and sequence. More than 100 members of this family have been identified in both Arabidopsis and rice. However, only a few of them have been functionally characterized, especially in rice. NACs play important roles in plant development, including pattern formation of embryos and flowers, formation of secondary walls, and development of lateral roots. NACs are also reported to participate in abiotic and biotic responses.
• Genetic improvement in drought tolerance in rice is the key to save water for sustainable agriculture. Drought tolerance is a complex trait and involves interplay of a vast array of genes. Several genotypes of rice have evolved features that impart tolerance to drought and other abiotic stresses.

Labs working on this gene

• National Key Laboratory of Crop Genetic Improvement, National Center of Plant Gene Research (Wuhan) and College of Life Science and Technology, Huazhong Agricultural University, Wuhan 430070, China
• College of Tobacco Science, Yunnan Agricultural University, Kunming, Yunnan, P. R. China
• Agricultural College, Henan University of Science and Technology, Luoyang, Henan, P. R. China