Transcription factors important in the regulation of salinity tolerance.

Abstract

Salt tolerant plants are able to survive in saline soils by the virtue of an array of channels and pumps that minimise sodium entry into roots and loading into the xylem, as well as the sequestration of sodium in the vacuole of the cells of both root and shoot. Regulation of genes involved in conferring salt tolerance is thought to occur via a network of transcription factors. In this project, the aim is to identify transcription factors that are important in regulating genes involved in salinity tolerance. Affymetrix Rice 57K GeneChip data from a previous project were used to analyse gene expression with and without salt stress in the shoots and roots of the salt sensitive Oryza sativa cultivar IR29 and the salt tolerant cultivars FL478, IR63731 and Pokkali. Transcription factors showing differential expression between the salt sensitive and salt tolerant cultivars were identified and confirmed by qRT-PCR. Six transcription factors with confirmed expression patterns were selected and transgenic rice plants were generated either constitutively or salt inducibly over-expressing each of the transcription factor coding sequences. Plants were also made expressing artificial microRNAs designed to reduce levels of transcripts of each transcription factor. The altered expression of five transcription factors, OsOrphan19, OsEREB67, OsbHLH17, OsLUX and OsMYB54 affected plant salinity tolerance, as evidenced by changes in Na⁺ and K⁺ accumulation and plant fresh weight. These five transcription factors show significant homology to other previously known stress responsive genes thus suggesting their involvement in plant stress responses. Further experiments such as chromatin immunoprecipitation sequencing and RNA-sequencing of transgenic plants need to be performed to identify the target promoters and downstream genes, respectively, to determine the precise role of these transcription factors in plant responses to salt stress.