The Evolution And Function Of The Pineapple SWEET Genes Family

Pineapple(Ananas comosus(L.)Merr.)belongs to the Bromeliaceae,which is one of the most important tropical and subtropics fruits in the world and the crucial economic crop in China.Sugar content of pineapple fruit is one of the important factors that determine the quality and yield.Fruits mainly accumulating sugar by carry out carbohydrate metabolism,and photosynthetic products are transported in the form of sucrose to the sink organ,providing energy to the growth and development of the sink organ.SWEETs(Sugars will eventually be exported transporters)are a group of recently identified sugar transporters in plants that play important roles in diverse physiological processes.However,currently,limited information about this gene family is available in pineapple(Ananas comosus).The availability of the recently released pineapple genome sequence provides the opportunity to identify SWEET genes in a Bromeliaceae family member at the genome level.In this study,the SWEET genes were identified by comparative genomics and provided a systematic description of SWEET genes using a set of bioinformatics approaches.Investigation utilized transcriptome data to analyze the expression patterns of different SWEET genes,and identified putative candidates with probable roles in the reproductive tissue development.The main findings were as follows:1.Based on the comparative genomics analysis,the Arabidopsis thaliana SWEET genes were employed as queries determine the SWEET gene family members in two pineapple cultivars.A total of 39 putative SWEET genes were obtained,included 18 different sequences in F153 varieties and 21 in MD2 varieties.Conserved domain search has shown that all 39 SWEETs harbored MtN3/saliva domain,and at least one ?-helical transmembrane(TM)domain.2.To infer the evolutionary relationships of SWEET proteins in two pineapple varieties,a total of 39 SWEET proteins,were used to construct the NJ(neighbor join)phylogenetic tree.The phylogenetic results revealed that all AnSWEET members could be separated into five subfamilies: clade I,II,III,IV,V.Most SWEET homologs showed similar clustering patterns in both F153 and MD2 varieties.The MD2 cultivar might have experienced additional expansion than the F153 cultivar.It is speculated that the two varieties may be experienced different evolutionary histories.3.A gene exon/intron structure analysis showed that the pineapple SWEET genes contained highly conserved exon/intron numbers,the most SWEETs were found to possess 5 introns.Furthermore,the first two exons were both very short for the SWEET genes,and might be easily lost over evolution.Beyond that,the number of intron in two varieties were compared that lied in the same branch of the phylogenetic tree and found that many of the AnmSWEET genes contain less than AnfSWEET genes.It is speculated that the MD2 varieties may be experienced most lost.4.Duplicate event analysis showed that WGD/segmental and fragment duplication were the main expansion way of SWEET genes.A total of 15 collinear SWEET gene pairs 22 SWEET genes were discovered among the two pineapple genomes.Phylogenetic analysis indicated that two counterparts of each gene pair were from the same clade.It is speculated that these genes may be present in pineapple ancestors and preserved during evolution.5.An analysis of public RNA-seq data and expression profiling showed that SWEET genes may be involved in fruit development and ripening processes.Among the 21 AnmSWEETs,12 genes showed expression in different stages of fruit development and ripening.AnmSWEET5 showed high expression in all tested stages.Furthermore,the expression of AnmSWEET21 and AnmSWEET6 exhibited a gradually down-regulated expression profile during fruit development.By contrast,the expression of AnmSWEET13 exhibited a gradually up-regulated expression profile.