Abiotic stress regulates expression of galactinol synthase genes post-transcriptionally through intron retention in rice
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Expression of the Galactinol synthase genes in rice is regulated through post-transcriptional intron retention in response to abiotic stress and may be linked to Raffinose Family Oligosaccharide synthesis in osmotic perturbation.
Galactinol synthase (GolS) is the first committed enzyme in raffinose family oligosaccharide (RFO) synthesis pathway and synthesizes galactinol from UDP-galactose and inositol. Expression of GolS genes has long been implicated in abiotic stress, especially drought and salinity. A non-canonical regulation mechanism controlling the splicing and maturation of rice GolS genes was identified in rice photosynthetic tissue. We found that the two isoforms of Oryza sativa GolS (OsGolS) gene, located in chromosomes 3(OsGolS1) and 7(OsGolS2) are interspersed by conserved introns harboring characteristic premature termination codons (PTC). During abiotic stress, the premature and mature transcripts of both isoforms were found to accumulate in a rhythmic manner for very small time-windows interrupted by phases of complete absence. Reporter gene assay using GolS promoters under abiotic stress does not reflect this accumulation profile, suggesting that this regulation occurs post-transcriptionally. We suggest that this may be due to a surveillance mechanism triggering the degradation of the premature transcript preventing its accumulation in the cell. The suggested mechanism fits the paradigm of PTC-induced Nonsense-Mediated Decay (NMD). In support of our hypothesis, when we pharmacologically blocked NMD, the full-length pre-mRNAs were increasingly accumulated in cell. To this end, our work suggests that a combined transcriptional and post transcriptional control exists in rice to regulate GolS expression under stress. Concurrent detection and processing of prematurely terminating transcripts coupled to repressed splicing can be described as a form of Regulated Unproductive Splicing and Translation (RUST) and may be linked to the stress adaptation of the plant, which is an interesting future research possibility.
KeywordsRice GolS Abiotic stress RUST Splicing Regulation
The project is supported by funds from Department of Biotechnology and the Raja Ramanna Fellowship Project of the Department of Atomic Energy, Government of India awarded to ALM, currently an INSA Senior Scientist. SM was supported by Fellowship from the Council of Scientific and Industrial Research (CSIR) and Department of Atomic Energy (DAE). SS was a Staff Scientist supported by DBT and Fast-Track young scientist scheme of Department of Science and Technology (DST), Government of India. AM is supported by the DBT project.
This study is funded by grants from the Department of Biotechnology (DBT654BT/AB/05/02/2007-III) and the Raja Ramanna Fellowship Project of the Department of Atomic Energy (D.O No. 10/25/2010/RRF-R & D-II/3118), both from the Government of India, awarded to ALM, currently an INSA Senior Scientist. SM and PB was supported by Fellowship from the Council of Scientific and Industrial Research (CSIR) and Department of Atomic Energy (DAE). AM is supported by the DBT project. SSG was a Staff Scientist supported by DBT and Fast-Track Young Scientist Scheme of Department of Science and Technology (DST), Government of India.
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Conflict of interest
The authors declare that they have no conflicts of interest.
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