Abstract
Basic helix-loop-helix (bHLH) transcription factors constitute one of the largest families in plants and are known to be involved in various developmental processes and stress tolerance. We report the characterization of a stress responsive bHLH transcription factor from stress adapted species finger millet which is homologous to OsbHLH57 and designated as EcbHLH57. The full length sequence of EcbHLH57 consisted of 256 amino acids with a conserved bHLH domain followed by leucine repeats. In finger millet, EcbHLH57 transcripts were induced by ABA, NaCl, PEG, methyl viologen (MV) treatments and drought stress. Overexpression of EcbHLH57 in tobacco significantly increased the tolerance to salinity and drought stress with improved root growth. Transgenic plants showed higher photosynthetic rate and stomatal conductance under drought stress that resulted in higher biomass. Under long-term salinity stress, the transgenic plants accumulated higher seed weight/pod and pod number. The transgenic plants were also tolerant to oxidative stress and showed less accumulation of H202 and MDA levels. The overexpression of EcbHLH57 enhanced the expression of stress responsive genes such as LEA14, rd29A, rd29B, SOD, APX, ADH1, HSP70 and also PP2C and hence improved tolerance to diverse stresses.
Highlights
The environmental stress signals such as drought, salinity, high temperature perceived by the plants results in diverse stress responses
The Basic helix-loop-helix (bHLH) EST obtained from finger millet stress cDNA library was characterized for its stress responsiveness through expression analysis under different stress stimuli such as drought, NaCl, polyethylene glycol (PEG), ABA and methyl viologen (MV) treatments
The drought stressed leaves analyzed for EcbHLH57 expression showed increase in transcript levels (1.3 fold) at 80 and 60% field capacities (FC) over water control (100% FC), the levels were reduced at 40% FC but no significant differences were observed between treatments (Fig 1A)
Summary
The environmental stress signals such as drought, salinity, high temperature perceived by the plants results in diverse stress responses. These responses are regulated by many complex mechanisms which are controlled by transcriptional regulation. Several stress responsive TFs belonging to APETELA2 (AP2), bHLH, bZIP, NAC, ZF, MYB and WRKY families have been well elucidated for their regulatory roles under various stress conditions. Transgenic plants overexpressing these groups of genes have shown improved tolerance to different stresses [4, 5, 6, 7].
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