- HsfAs not only responded to high temperature but also to oxidative stress, high salinity, chilling and other stresses.
- OsHsfA7 has an important role in root growth and development. OsHsfA7 may play a role as a member of natural defense system against high salinity and drought stresses.
- OSHsfA5 and OSHsfA7 transcripts were at correspondingly low levels in all tissues; while transcript levels of OSHsfA5 were lower in roots, those of OSHsfA7 were slightly higher in leaves.
Root morphology of the WT and OsHsfA7-OE transgenic plant seedlings was shown in Figure 1. OsHsfA7-OE plants exhibited longer young roots (including primary root and adventitious root) (Fig. 1A) but shorter and less lateral roots (Fig. 1B) and root hair (Fig. 1C) compared with the WT. Average radicle length of 5 d OsHsfA7-OE seedling was 3.7cm, and that of WT was only 1.5 cm, the results showed that the young roots of transgenic seedlings grew faster than the control. Moreover, the roots of OsHsfA7-OE at tillering stage were thicker, sparser, more wide distributed and almost no lateral roots compared with that of wild type.
1 over-expression of OsHsfA7 can improve salt resistance of transgenic rice:
- After irrigating with 200 mM NaCl for 10 d, leaf apex of WT plants became brown and dried, whereas over-expressing OsHsfA7 leaves remained green (Fig. 2B).
- Leaf REC and MDA content were lower in the transgenic lines than in the WT (Fig. 2E, F).
- Hydroponic seedlings were treated with 200 mM NaCl for 24 h then transferred to 1/2 MS solution for recovery. After 4 d, leaves of WT were completely curled and wilted, while those of OsHsfA7-OE were rolled only in the tip part (Fig. 2C).
- After 10 d recovery, leaves of WT were withered and almost all plants were completely dead, while most of the transgenic plants remained alive and only the leaf tips scorched(Fig. 2D).
2 thermo-tolerance and drought stress：
- To examine the tolerance to drought stress, three-week-old plants were withheld water for 10 d and then re-watered for additional 10 d. Both WT and transgenic plants suffered severe blast after un-watering (Fig. 3B).
- Whereas there was remarkable difference after re-watering. While most of the WT plant leaves showed further withered and could not be rescued, the majority of OsHsfA7-OE plants restored normal growth (Fig. 3C).
3 Meanwhile, we tested the thermo-tolerance of transgenic and WT plants at booting stage, no significant difference was found in seed setting rate after treatment.
4 However, the transcript levels of OSHsfA4b, OSHsfA5, OSHsfA7 and five OSHsfA2s were significantly up-regulated during early stages (OSHsfA2a, OSHsfA2c, OSHsfA2d, OSHsfA4b at 15 min, OSHsfA2d, OSHsfA2e, OSHsfA7 at 45 min and OSHsfA5 at 1.5 h) of heat stress exposure, with the effect gradually diminishing when prolonged heat stress.
5 short-term heat stress and calcium on HSF expression:
- OsHsfA7 has little or no expression when calcium and heat stress are given separately but showed some expression when both these treatments are combined.
6 PEG stress:
- OSHsfA2a, OSHsfA2e, OSHsfA3, OSHsfA4d, OSHsfA5 together with OSHsfA7 genes responded more drastically by PEG
7 Among the three Hsfs, OsHsfA7 was significantly upregulated in shoot (11.8-fold) and root(13.3-fold) after SDS. 
8 Expression of AtHsfA7a was reported to be elevated in cells during light stress. OsHsfA7 responded to all the four treatments(Heat,Salt,PEG,Cold).
9 OsHsfA2a, OsHsfA2c, OsHsfA2d, OsHsfA7, OsHsfA2f, OsHsfB1, OsHsfB2a and OsHsfB4c, genes showed high TA values during HS and OS treatments in Q-PCR.
10 Dheeraj Mittal et al. propose that OsHsfA2f and OsHsfA7 may be involved in the late response to the oxidative stress.
- OsHsfA7 shares 31.7% and 62.3% identity at the amino acid level with HsfA7 of Medicago and Sorghum. Phylogenetic analysis revealed that genetic relationship between Oryza sativa and Sorghum was closer.
- It was found that only OsHsp24.1 was up-regulated in the OsHsfA7-OE plants, while expressions of the other eight Hsp genes showed no obvious difference between WT and transgenic rice.
- Plants respond to heat stress by enhancing the expression of genes encoding heat shock protein (HSPs)genes through activation of heat shock factors (HSFs)
- Of 25 genes as OsHsf, 13 genes belong to Class A, 8 genes to Class B and remaining 4 to Class C type HSF.
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.
- Three class A proteins (OsHsfA2c, OsHsfA2d and OsHsfA9) show transactivation activity; however, two class A members(OsHsfA2a and OsHsfA7) containing AHA motifs lack activity.It is also possible that HSE specificity of OsHsfB4b changes via hetero-oligomerization with OsHsfA2a, OsHsfA7 and OsHsfB4c.
Labs working on this gene
- Key Laboratory for Crop Germplasm Innovation and Utilization of Hunan Province, Hunan Agricultural University
- College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha, 410128, China
- Department of Plant Molecular Biology, University of Delhi, South Campus, Benito Juarez Road, Dhaula Kuan, New Delhi 110 021, India
- Division of Health Sciences, Graduate School of Medical Science, Kanazawa University, Japan
- Crop Gene Engineering Key Laboratory of Hunan Province, Hunan Agricultural University, Furong District, Room 420, Life Science Building, Changsha (410128)
- Institute of Rice Science, Hunan Agricultural University, Changsha, 410128
- Directorate of Rice Research, Hyderabad, Andhra Pradesh, India
- Centre for Biotechnology, Institute of Science & Technology, Jawaharlal Nehru Technological University, Hyderabad, India
- Crop Gene Engineering Key Laboratory of Hunan Province, Hunan Agricultural University, Changsha City, Hunan Province, China
- 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.
- Liu A L, Liu C F, Zhang X W, et al. BMB Reports: Over-expression of OsHsfA7 enhanced salt and drought tolerance in transgenic rice[J]. Biochemistry and Molecular Biology Reports, 2013, 46(1): 31-36.
- Mittal D, Enoki Y, Lavania D, et al. Binding affinities and interactions among different heat shock element types and heat shock factors in rice (Oryza sativa L.)[J]. FEBS Journal, 2011, 278(17): 3076-3085.
- Liu A, Zou J, Zhang X, et al. Transcriptional Profiling of Class A Rice Heat Stress Transcription Factor Genes (OsHsfAs) under Abiotic Stress[J].
- Sailaja B, Anjum N, Prasanth V V, et al. Comparative Study of Susceptible and Tolerant Genotype Reveals Efficient Recovery and Root System Contributes to Heat Stress Tolerance in Rice[J]. Plant Molecular Biology Reporter, 2014: 1-13.
- Liu A L, Zou J, Zhang X W, et al. Expression profiles of class A rice heat shock transcription factor genes under abiotic stresses[J]. Journal of Plant Biology, 2010, 53(2): 142-149.
- 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.