Os08g0546800

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As a member of class B Hsfs(heat shock factors), OsHsfB2b (Oryza sativa) negatively regulates drought and salt tolerance in rice[1].

Annotated Information

Function

  • OsHsfB2b functions as a negative regulator in response to drought and salt stresses in rice, with its existing B3 repression domain (BRD) that might be necessary for the repressive activity.
  • Overexpression of OsHsfB2b significantly decreased drought and salt tolerance in transgenic plants, while the OsHsfB2b-RNAi plants enhanced tolerance under these stresses, OsHsfB2b may negatively regulate the abiotic stress tolerance in rice[1].
  • Wang et al. identified a total of 25 rice Hsf genes by genome-wide analysis of rice (Oryza sativa L.) genome, including the subspecies of O. japonica and O. indica. Proteins encoded by OsHsfs were divided into three classes according to their structures. Digital Northern analysis showed that OsHsfs were expressed constitutively. The expressions of these OsHsfs in response to heat stress and oxidative stress differed among the members of the gene family[2].

GO assignment(s): GO:0003677, GO:0003700, GO:0005634, GO:0043565

Mutation

  • Three independent overexpression lines (OE1, OE10 and OE12)
  • three independent RNAi lines (Ri1, Ri5 and Ri8)

Expression

Figure 1.Expression analysis of the OsHsfB2b gene by real-time PCR.(from reference [1]).
  • OsHsfB2b (Os08g0546800) was strongly induced in heat-tolerant rice cultivar 996 (indica) under heat stress[3]. The induction level of this gene was significantly higher than those of the other members of class B Hsfs, class C Hsfs and some members of class A Hsfs.
  • The expression of OsHsfB2b was induced by salt, polyethylene glycol (PEG), and ABA treatments after 2 h, and kept increasing at 24 h (Fig. 1a). The expression of OsHsfB2b was strongly induced by heat stress especially at very early stage and gradually reduced to lower increased level, but the expression was almost not affected by low-temperature treatment (Fig. 1b). The tissue-specific expression analysis indicated that OsHsfB2b expression was high in sheaths and panicles, medium expression in stems and leaves, but very

low in roots and seedlings (Fig. 1c). the promoter contains many putative stress response-related cis-elements, such as ABRE (4 hits), DRE (2 hits), MYB recognition site(MYBRS, 5 hits), MYC recognition site (MYCRS, 6 hits), and HSE (1 hit) (Fig. 1d)[1].

  • OsHsfB2b negatively regulates drought tolerance in rice[1]:
    • overexpressing OsHsfB2b significantly decreased drought tolerance while RNA interference of this gene improved drought tolerance in transgenic rice at the seedling stage.
  • OsHsfB2b negatively regulates salt stress tolerance in rice[1]：
    • overexpression of OsHsfB2b significantly decreased seed germination, while RNA interference of this gene improved seed germination under salt stress condition.
  • overexpression or RNA interference of OsHsfB2b gene had no significant effect on temperature tolerance[1].
  • The lower germination rate of overexpression lines and the higher germination rate of RNAi lines than that of wild-type seeds

under osmotic stress suggested that OsHsfB2b may have a negative regulatory effect on osmotic stress tolerance in rice.This effect was further confirmed in the postgermination stage rice seedling[1]. In a word, expression of OsHsfB2b was strongly induced by heat, salt, ABA and PEG treatments. Drought and salt tolerances were significantly decreased by OsHsfB2b overexpression, but were enhanced by RNA interference[1].

Evolution

Figure 2.Phylogenetic tree based on the amino acid sequence of the OsHsf genes.(from reference [4]).
Figure 3.Phylogenetic analysis of rice HSF genes.(from reference [5]).
  • Phylogenetic analysis showed that distinct groups of OsHsfs are class-wise distributed (Fig. 2). All class A2 OsHsfs (OsHsfA2a, OsHsfA2b, OsHsfA2c, OsHsfA2d and OsHsfA2e), OsHsfA1a, OsHsfA9 and Os06g22610 (the new OsHsf entry) were grouped in a single major clade. All class B OsHsfs showed divergence from a common point and were grouped with OsHsfA5,

OsHsfA4d and OsHsfA4b. All class C members showed a common divergence point in the evolutionary lineage and appeared much closer to OsHsfA3. OsHsfA7 and OsHsfA2f appeared to have diverged much early from this clade[4].

  • A significant divergence appears to have taken place in class A OsHsf members during the course of evolution. All duplicated OsHsf gene pairs were seen as sister clade with a distinct dichotomy, suggesting their recent evolutionary divergence[4].
  • To explore the evolution of the OsHSFs in the rice genome, an un-rooted tree was constructed from alignments of their full-length protein sequences (Fig. 3). It is seen that rice HSFs are clearly grouped into three major clades as per their A, B and C type with well-supported boot strap values. All class A HSFs are grouped in one single major clade with two distinct sub groups of A2, A3, A7 and A5,

A4, A9 and A1. All class B HSFs also grouped together and appear to have diverged from the type A subgroup having A1 in close proximity. Class C HSFs also make different group and appear closer to OsHsfA7. Therefore, it appears from the phylogenetic tree that one subgroup of class A HSF gave rise to class B and the other to class C. As expected, all the duplicated HSFs grouped together in the phylogenetic tree[5] (Fig. 3).

Knowledge Extension

Expression profiling showed that 22 OsHsf genes are induced by high temperature. Induction of 10 and 14 OsHsf genes was also noted against low temperature stress and oxidative stress, respectively. All OsHsf genes induced by oxidative stress were also induced by high temperature. On the other hand, induction of 6 and 1 OsHsf genes was noted to be exclusive to high and low temperature stresses, respectively. Seven OsHsf genes showed induced expression in response to all the three stresses examined. While in silico promoter analysis showed that OsHsf genes contain upstream regulatory elements corresponding to different abiotic stresses, there was lack of correlation noted between the in silico profiling of the elements and their corresponding transcript expression patterns[4].

  • Heat stress transcription factors (Hsfs) are the central regulators of defense response. They control the expression of heat shock proteins (HSPs) in plants by specific binding to the highly conserved heat shock element (HSE) characterized by palindromic motifs of nGAAn[4][6].
  • The rice HSF family is distributed on 10 of the 12 chromosomes; no HSF gene is present on chromosome 11 and 12. Maximum six HSF genes are present on chromosome 3. The position and direction of transcription (arrows) of each HSF gene are marked with the help of

International Rice Genome Sequencing Project (IRGSP) rice chromosome pseudomolecules. Six of the 25 rice HSFs are found to be segmentally duplicated and in three cases the orientation is also reversed. Both the HSFs found on chromosome 8 are segmentally duplicated with 2 of the HSF on chromosome 9, and all are class B HSF. In total, three class B, two class A and one class C HSF are segmentally duplicated. The single HSF present on chromosome 10 is also duplicated[5].

Labs working on this gene

  • Hunan Provincial Key Laboratory for Germplasm Innovation and Utilization of Crop, Hunan Agricultural University, Changsha 410128, Hunan, China
  • School of Life Science, Hunan University of Science and Technology, Xiangtan 411201, China
  • College of Life Science, Resources and Environment, Yichun University, Yichun 336000, China
  • College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha 410128, China

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Xiang J, Ran J, Zou J, et al. Heat shock factor OsHsfB2b negatively regulates drought and salt tolerance in rice[J]. Plant cell reports, 2013, 32(11): 1795-1806.
  2. ↑ Wang C, Zhang Q, Shou H. Identification and expression analysis of OsHsfs in rice[J]. Journal of Zhejiang University Science B, 2009, 10(4): 291-300.
  3. ↑ Zhang X, Li J, Liu A, et al. Expression profile in rice panicle: insights into heat response mechanism at reproductive stage[J]. PloS one, 2012, 7(11): e49652.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 Mittal D, Chakrabarti S, Sarkar A, et al. Heat shock factor gene family in rice: genomic organization and transcript expression profiling in response to high temperature, low temperature and oxidative stresses[J]. Plant Physiology and Biochemistry, 2009, 47(9): 785-795.
  5. ↑ 5.0 5.1 5.2 Chauhan H, Khurana N, Agarwal P, et al. Heat shock factors in rice (Oryza sativa L.): genome-wide expression analysis during reproductive development and abiotic stress[J]. Molecular Genetics and Genomics, 2011, 286(2): 171-187.
  6. ↑ Miller G A D, Mittler R O N. Could heat shock transcription factors function as hydrogen peroxide sensors in plants?[J]. Annals of Botany, 2006, 98(2): 279-288.

Structured Information

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