Abstract
The Dothideomycete fungus Mycosphaerella graminicola is the causal agent of Septoria tritici blotch, a devastating disease of wheat leaves that causes dramatic decreases in yield. Infection involves an initial extended period of symptomless intercellular colonisation prior to the development of visible necrotic disease lesions. Previous functional genomics and gene expression profiling studies have implicated the production of secreted virulence effector proteins as key facilitators of the initial symptomless growth phase. In order to identify additional candidate virulence effectors, we re-analysed and catalogued the predicted protein secretome of M. graminicola isolate IPO323, which is currently regarded as the reference strain for this species. We combined several bioinformatic approaches in order to increase the probability of identifying truly secreted proteins with either a predicted enzymatic function or an as yet unknown function. An initial secretome of 970 proteins was predicted, whilst further stringent selection criteria predicted 492 proteins. Of these, 321 possess some functional annotation, the composition of which may reflect the strictly intercellular growth habit of this pathogen, leaving 171 with no functional annotation. This analysis identified a protein family encoding secreted peroxidases/chloroperoxidases (PF01328) which is expanded within all members of the family Mycosphaerellaceae. Further analyses were done on the non-annotated proteins for size and cysteine content (effector protein hallmarks), and then by studying the distribution of homologues in 17 other sequenced Dothideomycete fungi within an overall total of 91 predicted proteomes from fungal, oomycete and nematode species. This detailed M. graminicola secretome analysis provides the basis for further functional and comparative genomics studies.
Highlights
Plant pathogenic fungi and oomycetes secrete an arsenal of proteins and metabolites during infection of their hosts
This predicted the total secretome for M. graminicola and contained 970 proteins
Septoria tritici blotch disease of wheat caused by Mycosphaerella graminicola represents a significant economic threat to global wheat production in the context of future food security concerns
Summary
Plant pathogenic fungi and oomycetes secrete an arsenal of proteins and metabolites during infection of their hosts. In many cases plants have evolved the capability to recognise either directly or indirectly these effectors through disease resistance (R) proteins and/or guardee proteins giving rise to the widely accepted ‘‘gene-forgene’’ model of effector triggered immunity [3] This frequently activates a particular defence response involving highly localised cell death, termed hypersensitive cell death, which is effective against biotrophic pathogens. For fungi which have a necrotrophic lifestyle, some of the small secreted effector proteins have been shown to target plant susceptibility (S) proteins encoded by homologues of resistance genes In these cases, the resulting S protein – effector interaction triggers widespread HR for the benefit of the pathogen. Both examples highlight that pathogens require a very specific and selective effector repertoire which enable them to infect their often restricted range of host plants and/or particular plant tissues, to cause disease and complete their lifecycle through asexual/sexual sporulation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
