The SWEET family genes in strawberry: Identification and expression profiling during fruit development

Abstract

The transport of sugar is essential for plant growth and development, tightly correlated with crop productivity and quality. SWEET (Sugar Will Eventually be Exported Transporters) is a family of sugar effluxer first reported a decade ago, whose significance has been reported in a dozen of plant species. Strawberry is an important crop developing striking fruits. Up to date, the involvement of SWEETs in strawberry is completely elusive. Current work focuses on the genome-wide identification of SWEET transporter coding genes in diploid strawberry (Fragaria vesca) and the expression analysis of octoploid strawberry (F. × ananassa) SWEET homoeologs in different vegetative and reproductive organs. A total of 20 candidate SWEET loci were identified in Fragaria vesca V4 genome via a local blast using the MtN3_slv motif (PF03083) against the protein database of FvH4.0.a2 version. Phylogenetic analysis indicated this family falling into four clades. These genes are distributed in all seven chromosomes except for Fvb1, and most members contain six exons divided by five introns, coding a protein with 235 to 310 aa and around 7 transmembrane helices. The spatio-temporal expression profiles of SWEET genes in different parts of fruit (cortex, pith and achenes) of cv. Benihoppe were explored and a set of candidate SWEET genes invoved in sugar transport in strawberry fruits were identified, such as FvSWEET1, -2a, -7, -9a, -9c, -10, and -11. Our results provide a good foundation for further functional investigation of SWEETs in strawberry fruit quality formation and other developmental processes as well as responses to pathogens and abiotic stresses. The information of SWEETs in strawberry also has a reference value for other Rosaceae plants.