SWEET Gene Family in Medicago truncatula: Genome-Wide Identification, Expression and Substrate Specificity Analysis

Abstract

SWEET (Sugars Will Eventually be Exported Transporter) proteins mediate the translocation of sugars across cell membranes and play crucial roles in plant growth and development as well as stress responses. In this study, a total of 25 SWEET genes were identified from the Medicago truncatula genome and were divided into four clades based on the phylogenetic analysis. The MtSWEET genes are distributed unevenly on the M. truncatula chromosomes, and eight and 12 MtSWEET genes are segmentally and tandemly duplicated, respectively. Most MtSWEET genes contain five introns and encode proteins with seven transmembrane helices (TMHs). Besides, nearly all MtSWEET proteins have relatively conserved membrane domains, and contain conserved active sites. Analysis of microarray data showed that some MtSWEET genes are specifically expressed in disparate developmental stages or tissues, such as flowers, developing seeds and nodules. RNA-seq and qRT-PCR expression analysis indicated that many MtSWEET genes are responsive to various abiotic stresses such as cold, drought, and salt treatments. Functional analysis of six selected MtSWEETs in yeast revealed that they possess diverse transport activities for sucrose, fructose, glucose, galactose, and mannose. These results provide new insights into the characteristics of the MtSWEET genes, which lay a solid foundation for further investigating their functional roles in the developmental processes and stress responses of M. truncatula.

Systematic Genome-Wide Study and Expression Analysis of SWEET Gene Family: Sugar Transporter Family Contributes to Biotic and Abiotic Stimuli in Watermelon

“…In Medicago truncatula [25], cucumber [16], banana [13], Brassica rapa [6], cabbage [17], tomato [19], soybean [23], rubber tree [18], cotton [54], and pear [55], more than half of the SWEET members have six exons and five introns, suggesting that during evolution the molecular features of SWEET genes were highly conserved. Here, the gene structure analysis of ClaSWEET genes indicated that 12 members (about 54.5%) harbored six exons and five introns.…”

Distinct genetic basis for root responses to lipo-chitooligosaccharide signal molecules from different microbial origins

“…Similarly, two putative auxin efflux carriers, similar to the PIN-like PILS 5 and 7 proteins from Arabidopsis (Sauer and Kleine-Vehn, 2019) were found associated with the primary root response after 5 days in response to Nod-LCOs. For the root growth response to Fung-LCOs at 5 days, we also identified the MtSWEET3c locus that was shown to transport mannose and sucrose and to be expressed in Medicago nodules or roots upon abiotic stress (Hu et al, 2019).…”

Sugar transporters of the SWEET family and their role in arbuscular mycorrhiza

“…It is therefore impossible to speak strictly about the clade division of the SWEET genes for the types of the transferred substrate (see Suppl. Material 1) (Hu B. et al, 2019).…”

“…The intron-exon structure of the SWEET genes may also vary notably (Cao et al, 2019). Most of the MtSWEET genes (in M. truncatula) contain 5 introns, excluding the genes MtSWEET4, MtSWEET6, MtSWEET7 and MtSWEET13 which include 4 introns, and MtSWEET2b which contains 16 introns (Hu B. et al, 2019). The structure of the M. truncatula SWEET proteins is also heterogeneous: most contain 7 TMHs, but MtSWEET4 and MtSWEET11 have 6 TMHs, and MtSWEET2b contains 15 TMHs instead of 7 (Hu B. et al, 2019).…”