Identification and expression analysis of SoSWEET protein family genes in spinach

Based on the existing spinach genome information, 16 members of spinach SoSWEET protein family were screened and identified by bioinformatics methods. They were named SoSWEET1-SoSWEET16 according to their positions on chromosomes. The number of amino acids ranges from 648 to 1 140, the molecular weight ranges from 54 070.32 to 95 868.64 u, and the isoelectric point (pI) ranges from 5.06 to 5.19. The results of subcellular localization prediction showed that six SoSWEET proteins are located in the membrane, and five SoSWEET proteins are located in the endoplasmic reticulum, and membrane and endoplasmic reticulum, respectively. The phylogenetic tree analysis divided SoSWEET proteins into four subfamilies. Based on the phylogenetic tree, the gene structure, conserved motifs and cis-acting regulatory elements were analyzed further. Ten highly conserved motifs were identified, among which all the spinach SoSWEET proteins contained motifs 1, 2 and 4, constituting the most highly conserved part of spinach SoSWEET proteins. All members of the spinach SoSWEET proteins contained MtN3_slv and PQ-loop superfamily domains. The majority of SoSWEET protein family genes contain 5 introns, and the promoter contained cis-acting elements including light response, growth and development response, plant hormone response and stress response. The gene expression analysis showed that all SoSWEET genes were expressed in roots, stems, leaves and petioles, and downy mildew infecting. Collectively, These results provide an important reference for further studies on the functions of SoSWEET family genes in spinach.