Comparative gene expression of OsSWEETs from various rice genotypes during the development of bacterial blight as induced by the most virulent Race 4 of Xanthomonas oryzae pv. oryzae

Sugars are caloric carbohydrate compound found in nature, such as fruits and vegetables, and are required by all organisms. During the phloem loading process, SWEET efflux sucrose from phloem parenchyma cells and then transports it to the sieve element-companion cell complex (SE/CC) via active proton-coupled sucrose transporters (SUTs). There are 21 SWEETs identified in rice that play important roles in sugar efflux, signal transduction, plant growth and development, and biotic and abiotic stress tolerance. TALE proteins are pathogen-produced effectors that interact with host susceptibility genes and induce OsSWEET proteins. In this study, genetic variations in the promoter region of OsSWEET11, OsSWEET13 and OsSWEET14 are examined in 20 genotypes grown in India. Further sequence analysis of three genotypes having extreme response (resistance and susceptibility) to bacterial blight revealed that the promoter of the resistant genotype Pusa basmati 1692 is more closely clustered with the xa13, xa25 resistance genes than compared to susceptible genotype Pusa basmati 1. Relative gene expression studies showed that upon Xoo inoculation, the fold expression of clade III OsSWEET genes, namely OsSWEET11, OsSWEET13, OsSWEET14 and OsSWEET15 increases in cultivars IR24, Pusa Basmati1 and Improved Pusa Basmati1. Intriguingly, after Xoo challenge inoculation, OsSWEET15 expression was found to be increased along with other major OsSWEET genes, implying that it could be a novel target for a bacterial blight pathogen.