Identification Of Maize Sugar Transporter Protein Gene Families And Analysis Of Their Evolution And Expression

Photosynthesis produces carbohydrates,which are the basis of plant growth and development,such as sucrose,glucose,fructose and sugar alcohols,which can be transported from the "source" end to the "reservoir" end of the plant,such as roots,pistils,stamens and seeds,to supply energy and substances;and They can also be used as signaling molecules to regulate plant growth and development,or as osmoregulatory substances to alleviate plant damage under abiotic stresses.The transport of these soluble sugars between plant tissues,organs and cells is mediated by different types of glycotransport protein families,which have many members and complex evolutionary mechanisms.Maize(Zea mays L.)is one of the oldest and most important crops in the world and has an important place in our agricultural production.In this study,based on the identification of sugar transporter proteins in the maize genome database using comparative genomics,we conducted preliminary studies on their phylogeny,evolutionary analysis and functions,which not only laid the foundation for exploring the functions of maize sugar transporter protein family genes,but also enriched the maize resistance breeding gene resource pool.It is of theoretical guidance for the improvement of nutritional quality of maize and the enhancement of plant stress tolerance.The main results are as follows.1.98 sugar transporter proteins were identified in the whole maize genome,all belonging to the Mt N3＿slv and MFS superfamilies,which were classified according to sequence structural features and substrate specificity: SWEET family: with bidirectional transport of sucrose and SUT family,with the ability to transport disaccharides(mainly sucrose),has 7 members;MST family,with the ability to transport monosaccharides,is divided into 7 subfamilies: STP which transports hexose,has 23 members;PMT family:which transports polyols,has 20 members;and VGT family: glucose transporters with two members;ERD family: a family of nine members with the ability to transport small molecules such as soluble sugars and proline;in addition,INT,p Glc T and TMT family have the ability to transport inositol and proline,respectively.which have the ability to transport inositol,glucose,and monosaccharide,respectively,both contain four members.By constructing an evolutionary tree of sugar transporter proteins in the monocotyledonous plant maize,rice,and the dicotyledonous plant Arabidopsis,the gene families of sugar transporter proteins in maize and rice are relatively close in homology and relatively distant from Arabidopsis,suggesting that the ancestors of some genes of the maize sugar transporter protein family arose before the differentiation of land plants.Expansion of maize genes occurred in the SWEET,STP,and PMT,whereas gene loss occurred in the ERD.2.Analysis of the gene structures and sequences of the maize sugar transporter protein family subfamilies revealed that the exons and introns of the maize sugar transporter protein subfamily members were similarly distributed and had the same conserved motifs,except for three members in the STP and one member each in the SUT,PMT,and INT whose gene structures differed significantly from those of the other members.The variation in gene length was mainly due to the insertion and deletion of introns or fusion of exons.The chromosomal localization results showed that the maize sugar transporter protein family genes were distributed on 10 chromosomes,but the number and location were uneven.25 members of the SWEET were distributed on 10 chromosomes;while two members of the VGT were both located on chromosome 5.Gene tandem duplication and chromosomal fragment duplication were the main forms of doubling and expansion of the zeose transporter protein family: the SWEET had 1 pair of tandem duplication and 5 pairs of fragment duplication;the SUT had no tandem duplication and only 3 pairs of fragment duplication;the MST had 8 pairs of tandem duplication and 12 pairs of fragment duplication.And the number of duplication events varied widely among different subfamilies,with 5 pairs of tandem duplication genes and 3 pairs of fragment duplication genes in the PMT,involving 14 genes;while there were no duplication events in the VGT,TMT,and INT.4.The prediction of the evolutionary rate and relative divergence time of sugar transporter protein family genes by Ka/Ks revealed that only one gene in the STP,PMT,and ERD,respectively,had Ka/Ks greater than 1 for positive selection,and the protein structure and function might be changed,which in turn would lead to changes in gene environmental adaptations and accelerated gene evolution.5.Analysis of cis-acting elements revealed that maize sugar transporter protein family genes have multiple abiotic stress as well as phytohormone-responsive acting elements.The expression patterns of maize sugar transporter protein genes under drought,salt and cadmium stresses as well as exogenous ABA were detected and analyzed by q PT-PCR,and most of the MST genes were found to respond rapidly.This indicates that maize sugar transporter protein family genes have important roles in biotic and abiotic stress response.