| The study in Carbohydrate metabolism of plant is the important aspecte of ecology, which brings the new opportunities for agriculture development. Sugarcane is one of the most important sugar crop in the world, and contributes about 80% of sugar and raw materials for ethanol fermentation worldwide. Increasing efforts in molecular biological studies have been performed for improving the sugar yield and other important agronomic traits in sugarcane. However, due to complicated genomes of sugarcane, it is still challenging to investigate the genetic basis of traits, including the key traits such as sugar accumulation. Sugar transporter are critical for both phloem loading in source tissue and sugar uptaking in sink tissue, and thus are considered to be the control points for regulating sugar storage. But genomic study for sugarcane sugar transporter superfamilies has not been reported up to date. In this study, we identified the sugar transporter genes by comparative genomics and analyzed the gene function by gene expression profiling.(1) By combinted comparative genomics with bacterial artificial chromosomes (BACs) resource,55 sugar transporter genes were identified and characterized in S.spontaenum. According to the characters of sequence structure, these 55 sugar transporter genes can be divided into nine family.15,13,7 members were identified in ployol transporter family (PLT), hexose transporter family (HXT) and early response to dehydrate family (SFP), respectively. And both putative monosaccharide sensing protein (MST) family and sucrose transporter (SUT) family had 6 members. both inositol transporter family (INT) and tonoplast monosaccharide transporter family (TMT) contained 3 members, and vacuolar glucose transporter family (VGT) and plastid glucose transporter family (pGLcT) both only have sinlge member.(2) The sugar transporter genes superfamily from classic monocot (Musa nana Lour., Oryza sativa, Sorghum bicolor, Saccharum) and dicot (Arabidopsis thaliana, Vitis vinifera) species were selected for the phylogenetic analysis. Phylogenetic analyses revealed that the gene families expansion caused by gene duplication, which occurred in SFP, PLT, MST and INT families in the process of the evolution. Interestingly, the SsHXT13 had the closer evolutionary relationship with banana HXT genes, indicating that the evolution rate of SsHXT13 is different with that of speciation. Forthermore, the analysis of the gene structure suggested that PLT and MST family may accompanied with the phenomenon of gene sequence lose and exon fusions in the process of evolution.In addition, a comprehensive analysis for SUTs were performed for gene allelic haplotypes, phylogenetic relationships, gene structure, and gene expression pattern in Saccharum species (Saccharum officinarnum, Saccharum spontaenum, Saccharum robustum). The results revealed that SsSUT5 and SsSUT6 were recent duplication genes companied by rapid evolution, while, SsSUT2 and SsSUT4 were the ancient members in the families. Gene size extensions caused by sequence insertions in introns were observed in the SUT families. Despite the high polyploidy level, the examined SUTs exhibited conserved gene structures and amino acid sequences among the allelic haplotypes.(3) The gene expression of the sugar transporter were analyzed based on FPKM values which were derived from RNA-seq. PLT3 had predominant expression in the PLT family of Saccharum species and Saccharum hybrid, suggesting that the gene may play an important role in phloem loading of polyol in the early stage of sugar accumulation. HXT13, HXT12, HXT2 and HXT8 were higher expressed genes in HXT family, they were highly expressed in seedling leaves of three Saccharum species and hybrid cultivar and all the examined tissues of mature stage of hybrid cultivar and S. officinarnum, indicated that these genes may play a role in loading and unloading of hexose in source tissues and sink tissuess, respectively. TMT1, MST6 and INT3 were predominant expressional member in these three gene families. Those result indicates that TMT1 might plays an important role in the transport of hexose in vacuole. The seedings of Saccharum species and hybrid cultivar were treated with hormone (GA,ABA, IAA) after 24h. The gene expression profiles were analyzed for the seeding plant with hormone treatment. PLT3 was revealed to be regulated by hormone stress. In SFP family, the expression of SFP3 may be induced by aging in the evidence of detected in all tissues of mature stage of Saccharum species and hybrid cultivar, and SFP8 may be related to the resistance of the seedling sugarcane as it exhibited a high expression level in the stem of seedling stage of S.spontaenum. INT3 exhibited a highly expression in all examined mature tissues, which indicated that the gene may comtributes to both inositol loading and unloading in phloem of source/sink organ. MST4 were undetectable in all tissues, suggesting that the MST4 gene may exists a function redundancy. SUT3 could be a low active member in the family because it is undetectable in our study, but it might not be a pseudogene because it harbored integrated gene structure. SUT1 and SUT4 were the main members for the sucrose transporter, while, these SUTs had sub-functional divergence in response to sucrose accumulation and plant development in Saccharum. |
PDF Full Text Request