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Background: Invertases (INVs) are key enzymes regulating sucrose metabolism and are here revealed to be involved in responses to environmental stress in plants. To date, individual members of the invertase gene family and their expression patterns are unknown in sugarcane due to its complex genome despite their significance in sucrose metabolism. Results: In this study, based on comparative genomics, eleven cDNA and twelve DNA sequences belonging to 14 non-redundant members of the invertase gene family were successfully cloned from sugarcane. A comprehensive analysis of the invertase gene family was carried out, including gene structures, phylogenetic relationships, functional domains, conserved motifs of proteins. The results revealed that the 14 invertase members from sugarcane could be clustered into three subfamilies, including 6 neutral/alkaline invertases (ShN/AINVs), and 8 acid invertases (ShAINVs). Faster divergence occurred in acid INVs than in neutral/alkaline INVs after the split of sugarcane and sorghum. At least a one-time gene duplication event was observed to have occurred in the four groups of acid INVs, whereas ShN/AINV1 and ShN/AINV2 in the ß8 lineage were revealed to be the most recently duplicated genes among their paralogous genes in the ß group of N/AINVs. Furthermore, comprehensive expression analysis of these genes was performed in sugarcane seedlings subjected to five abiotic stresses (drought, low temperature, glucose, fructose, and sucrose) using Quantitative Real-time PCR. The results suggested a functional divergence of INVs and their potential role in response to the five different treatments. Enzymatic activity in sugarcane seedlings was detected under five abiotic stresses treatments, and showed that the activities of all INVs were significantly inhibited in response to five different abiotic stresses, and that the neutral/alkaline INVs played a more prominent role in abiotic stresses than the acid INVs. Conclusions: In this study, we determined the INV gene family members of sugarcane by PCR cloning using sorghum as a reference, providing the first study of the INV gene family in sugarcane. Combining existing INV gene data from 7 plants with a comparative approach including a series of comprehensive analyses to isolate and identify INV gene family members proved to be highly successful. Moreover, the expression levels of INV genes and the variation of enzymatic activities associated with drought, low temperature, glucose, fructose, and sucrose are reported in sugarcane for the first time. The results offered useful foundation and framework for future research for understanding the physiological roles of INVs for sucrose accumulation in sugarcane. [ABSTRACT FROM AUTHOR]

Background: Sugarcane is an economically important crop contributing to about 80 % of the world sugar production. Increasing efforts in molecular biological studies have been performed for improving the sugar yield and other relevant important agronomic traits. However, due to sugarcane's complicated genomes, it is still challenging to study the genetic basis of traits, such as sucrose accumulation. Sucrose transporters (SUTs) are critical for both phloem loading in source tissue and sucrose uptaking in sink tissue, and are considered to be the control points for regulating sucrose storage. However, no genomic study for sugarcane sucrose transporter (SsSUT) families has been reported up to date. Results: By using comparative genomics and bacterial artificial chromosomes (BACs), six SUT genes were identified and characterized in S. spontaenum. Phylogenetic analyses revealed that the two pairs SsSUTs (SsSUT1/SsSUT3 and SsSUT5/SsSUT6) could be clustered together into two separate monocot specific SUT groups, while SsSUT2 and SsSUT4 were separated into the other two groups, with members from both dicot and monocot species. Gene structure comparison demonstrated that the number and position of exons/introns in SUTs were highly conserved among the close orthologs; in contrast, there were variations among the paralogous SUTs in Sacchuarm. Though with the high polyploidy level, gene allelic haplotype comparative analysis showed that the examined four SsSUT members exhibited conservations of gene structures and amino acid sequences among the allelic haplotypes accompanied by variations of intron sizes. Gene expression analyses were performed for tissues from seedlings under drought stress and mature plants of three Saccharum species (S.officinarnum, S.spotaneum and S.robustum). Both SUT1 and SUT4 expressed abundantly at different conditions. SUT2 had similar expression level in all of the examined tissues, but SUT3 was undetectable. Both of SUT5 and SUT6 had lower expression level than other gene member, and expressed stronger in source leaves and are likely to play roles in phloem loading. In the seeding plant leave under water stress, four genes SUT1, SUT2, SUT4 and SUT5 were detectable. In these detectable genes, SUT1 and SUT4 were down regulated, while, SUT2 and SUT5 were up regulated. Conclusions: In this study, we presented the first comprehensive genomic study for a whole gene family, the SUT family, in Saccharum. We speculated that there were six SUT members in the S. spotaneum genome. Out of the six members, SsSUTs, SsSUT5 and SsSUT6 were recent duplication genes accompanied by rapid evolution, while, SsSUT2 and SsSUT4 were the ancient members in the families. Despite the high polypoidy genome, functional redundancy may not exist among the SUTs allelic haplotypes supported by the evidence of strong purifying selection of the gene allele. 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. [ABSTRACT FROM AUTHOR]