Abstract
Understanding the mechanism of photosynthate transfer at symbiotic interface by fungal monosaccharide transporter is of substantial importance. The carbohydrate uptake at the apoplast by the fungus is facilitated by PiHXT5 hexose transporter in root endophytic fungus Piriformospora indica. The putative PiHXT5 belongs to MFS superfamily with 12 predicted transmembrane helices. It possess sugar transporter PFAM motif (PF0083) and MFS superfamily domain (PS50850). It contains the signature tags related to glucose transporter GLUT1 of human erythrocyte. PiHXT5 is regulated in response to mutualism as well as glucose concentration. We have functionally characterized PiHXT5 by complementation of hxt-null mutant of Saccharomyces cerevisiae EBY.VW4000. It is involved in transport of multiple sugars ranging from D-glucose, D-fructose, D-xylose, D-mannose, D-galactose with decreasing affinity. The uncoupling experiments indicate that it functions as H+/glucose co-transporter. Further, pH dependence analysis suggests that it functions maximum between pH 5 and 6. The expression of PiHXT5 is dependent on glucose concentration and was found to be expressed at low glucose levels (1 mM) which indicate its role as a high affinity glucose transporter. Our study on this sugar transporter will help in better understanding of carbon metabolism and flow in this agro-friendly fungus.
Highlights
Mycorrrhiza represents 400–100 million year of plant–fungus co-evolution due to nutritional dependency on each other
Blastx search of first P. indica (Genus ID: 65672) genome sequencing project3 using already characterized fungal hexose transporters such as GiMST2 from G. intraradices, GpMST1 from G. pyriformis, ScHXT1 from S. cerevisiae and TbHXT1 from Tuber borchii as query, a total of 19 putative sugar transporter sequences were identified in P. indica genome
Based on these data three sequences were rejected. These 16 putative sugar transporter sequences were further analyzed by SACS HMMTOP program for their membrane topology, we found that nine out of 16 protein sequences were showing typical MFS transporter membrane arrangement with 12 transmembrane helices, with a long intracellular loop between helix 6 and 7 and cytosolic N and C-terminal
Summary
Mycorrrhiza represents 400–100 million year of plant–fungus co-evolution due to nutritional dependency on each other. It has been credited with the most predominant association (70–90% of terrestrial plant species) in nature (Smith and Read, 2010). P. indica has several beneficiary effects on their host plants which include nutrient transport like phosphate, increase in biomass and grain yield and provide resistance to host plant against various abiotic and biotic stresses
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