Genome wide investigation and transcriptional profiling of SWEET genes in two contrasting cultivars of foxtail millet under abiotic stresses

Abstract

The SWEET (Sugars will eventually be exported transporter) gene family is an important class of sugar transporters that regulates diverse aspects of plant physiology such as apoplastic phloem loading, plant-pathogen interactions and plant responses to abiotic stresses. While majority of the studies on SWEET family in plants have been performed in C3 species, there are limited reports on C4 plants. In this study we conducted genome wide investigation of the SWEET gene family in foxtail millet, a naturally stress tolerant C4 crop. In-silico analysis identified 24 SWEET genes in foxtail millet genome that were classified into 4 distinct clades. Domain analysis revealed the presence of conserved MtN3_slv/PQ-loop domains in all identified SWEET proteins. Interestingly, many SWEET proteins also harboured the prokaryotic SemiSWEET/PQ-loop domain suggesting an evolutionary link to their prokaryotic Semi-SWEET ancestors. In-silico analysis predicted the presence of abscisic acid and drought responsive cis-elements in the promoter region of SWEET genes. Transcriptional analysis under control, drought, and salinity stress revealed differential expression patterns of SWEET genes in stress resistant and stress susceptible foxtail millet cultivars. Moreover, the differential expression of SWEET genes altered the soluble sugar content in leaves and roots under stress conditions suggesting altered carbon re-allocation between source and sink tissues. This study significantly advances our understanding of the SWEET gene family in C4 plants, particularly in foxtail millet, and provides insights into its role in stress tolerance mechanisms and carbohydrate re-allocation under stress conditions.