Identification of SUTs Family in Sweet Orange and Preliminary Analysis of SUT2 Function in Response to Xcc Induced
Citrus canker disease is a bacterial disease that harms citrus industry.The pathogen colonizes in the intercellular space,and the nutrients needed for its proliferation mainly come from the carbohydrate supplied by regulating the host sugar transporters.Sucrose Transporters(SUC/SUT)belong to a class of sugar transporters widely existing in plants,it plays an important role in the interaction between plants and pathogens.To explore the role of SUTs family in Citrus response to Xanthomonas citri subsp.citri(Xcc)infection.Firstly,seven SUTs were identified by bioinformatics analysis,distributed on five chromosomes,containing 4 to 13 exons,encoding 348 to 606 amino acids.The protein molecular weight(kD)was 38 626.32 to 64 921.00,the theoretical isoelectric point(pI)was 5.42 to 9.09,and the hydrophobic protein was 70％basic.According to the conserved motif of SUTS gene in orange,it was divided into branches 2,3 and 4.Secondly,by inoculating the susceptible germplasm Bingtang Orange and resistant germplasm Citron C-05 with Xcc,the results of real-time quantitative PCR showed that SUT2 was up-regulated in the leaves of Bingtang Orange induced by Xcc,but had no signifi-cant change in the leaves of Citron C-05.There was no significant change in other SUTs induced by Xcc in Bingtang Orange and Citron C-05.Amino acid sequence alignment of SUT2 homologous gene in Bingtang Or-ange and Citron C-05 showed 98.5％similarity.Analysis of cis-acting elements of promoter of SUT2 between the two germplasms showed little difference in species and number,and only specific motif Ⅰ(root specific com-ponents)were found in Bingtang Orange.The results of transient overexpression of SUT2 in susceptible Bing-tang Orange and resistant germplasm Citron C-05 showed that the symptoms of water stain were more obvious in overexpression area of leaves of both germplasms than that of control P0,and the content of Xcc per unit leaf area was significantly higher than that of control P0,suggesting that SUT2 protein had a significant promoting ef-fect on the growth of Xcc.
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