Patil G, Valliyodan B, Deshmukh R, Prince S, Nicander B, Zhao M, Sonah H, Song L, Lin L, Chaudhary J, Liu Y, Joshi T, Xu D, Nguyen HT.

BMC Genomics. 2015 Jul 11;16:520. doi: 10.1186/s12864-015-1730-y.

http://www.ncbi.nlm.nih.gov/pubmed/26162601

Abstract

BACKGROUND:

SWEET (MtN3_saliva) domain proteins, a recently identified group of efflux transporters, play an indispensable role in sugar efflux, phloem loading, plant-pathogen interaction and reproductive tissue development. The SWEET gene family is predominantly studied in Arabidopsis and members of the family are being investigated in rice. To date, no transcriptome or genomics analysis of soybean SWEET genes has been reported.

RESULTS:

In the present investigation, we explored the evolutionary aspect of the SWEET gene family in diverse plant species including primitive single cell algae to angiosperms with a major emphasis on Glycine max. Evolutionary features showed expansion and duplication of the SWEET gene family in land plants. Homology searches with BLAST tools and Hidden Markov Model-directed sequence alignments identified 52 SWEET genes that were mapped to 15 chromosomes in the soybean genome as tandem duplication events. Soybean SWEET (GmSWEET) genes showed a wide range of expression profiles in different tissues and developmental stages. Analysis of public transcriptome data and expression profiling using quantitative real time PCR (qRT-PCR) showed that a majority of the GmSWEET genes were confined to reproductive tissue development. Several natural genetic variants (non-synonymous SNPs, premature stop codons and haplotype) were identified in the GmSWEET genes using whole genome re-sequencing data analysis of 106 soybean genotypes. A significant association was observed between SNP-haplogroup and seed sucrose content in three gene clusters on chromosome 6.

CONCLUSION:

Present investigation utilized comparative genomics, transcriptome profiling and whole genome re-sequencing approaches and provided a systematic description of soybean SWEET genes and identified putative candidates with probable roles in the reproductive tissue development. Gene expression profiling at different developmental stages and genomic variation data will aid as an important resource for the soybean research community and can be extremely valuable for understanding sink unloading and enhancing carbohydrate delivery to developing seeds for improving yield.

Fig. 5:  Expression profiles of soybean SWEET genes in different tissues.aHierarchical cluster of expression profiles from two RNA-seq datasets in 24 tissues covering the whole life cycle of soybean (Williams 82). Sources of the samples are as follows: Dataset 1 - YL (young leaves), FL (flower), PD.1 cm (one cm pod), PS.10d (pod shell 10 Days After Flowering (DAF)), PS.14d (pod shell 14DAF), S.10d (seed 10DAF), S.14d (seed 14 DAF), S.21d (seed 21DAF), S.25d (seed 25DAF), S.28d (seed 28DAF), S.35d (seed 35DAF), S.42d (seed 42DAF), R1 (root), and Nod (nodule); Dataset 2 – GSS (globular stage whole seed), HRT (heart stage), COT (cotyledonary stage), EM (early maturation), DWS (dry whole seed), LF (leaf), R2 (root), STM (stem), FB (floral bud), and SDL (seedling). bExpression pattern of 52GmSWEETgenes. Bars show the expression of all genes in different developmental stages from both datasets. For simplicity, the datasets were marked with vegetative and reproductive stages.cqRT-PCR analysis of 21 selectedGmSWEETgenes in pedicel, pod, and seed tissues