Aquaporins in magnaporthe oryzae

The Ascomycete fungus Magnaporthe oryzae is the causative agent of Rice Blast, and has become the predominant model organism for study of fungal phytopathogens and other appressorium-forming fungi. I identified and attempted to elucidate the function of the six aquaporin genes in the M. oryzae genome. These small membrane channels have been implicated in the transport of water, glycerol, and a variety of other small molecules. We speculated that these functions might be important in the formation of the appressorium – a specialised infection structure that relies on the generation of turgor. The role of these proteins in general fungal biology is poorly understood, and this project endeavoured to correct this gap. A phylogenetic analysis of aquaporins in extant fungi revealed the significant expansion of this gene family in Pezizomycete and Basidiomycete fungi, with up to 17 genes in some species. I characterised the expression pattern of the six identified aquaporins in the M. oryzae genome during pathogenic development and found there to be substantial up-regulation co-incident with appressorial turgor generation. Single knock-outs of each aquaporin gene were fully pathogenic, with normal infection-related development and axenic growth. I speculated that the absence of a strong phenotype may have been caused by functional redundancy, and used qRT-PCR investigate the incidence of transcriptional up-regulation of remaining family members in the knock-out backgrounds. This uncovered a putative reciprocal relationship between two genes MoAQP1 and MoAQP2, suggesting that deletion of one results in up-regulation of the other. I subsequently tested the substrate permeability of this gene pair and found them to be permeable to hydrogen peroxide. However, deletion of one of these genes did not appear to affect the rate of flux of hydrogen peroxide across the plasma membrane. My attempt to characterise the cellular localisation of these proteins using GFP fusions was largely unsuccessful with the exception of a single gene, MoAGP2, which appears to be located on the endoplasmic reticulum.