Abstract
Wheat leaf rust, caused by the basidiomycete Puccinia triticina, can cause yield losses of up to 20% in wheat producing regions. During infection, the fungus forms haustoria that secrete proteins into the plant cell and effect changes in plant transcription, metabolism, and defense. It is hypothesized that new races emerge as a result of overcoming plant resistance via changes in the secreted effector proteins. To understand gene expression during infection and find genetic differences associated with races, RNA from wheat leaves infected with six different rust races, at 6 days post inoculation, was sequenced using Illumina. As P. triticina is an obligate biotroph, RNA from both the host and fungi were present and separated by alignment to the P. triticina genome and a wheat EST reference. A total of 222,571 rust contigs were assembled from 165 million reads. An examination of the resulting contigs revealed 532 predicted secreted proteins among the transcripts. Of these, 456 were found in all races. Fifteen genes were found with amino acid changes, corresponding to putative avirulence effectors potentially recognized by 11 different leaf rust resistance (Lr) genes. Twelve of the potential avirulence effectors have no homology to known genes. One gene had significant similarity to cerato-platanin, a known fungal elicitor, and another showed similarity to fungal tyrosinase, an enzyme involved in melanin synthesis. Temporal expression profiles were developed for these genes by qRT-PCR and show that the genes expression patterns were consistent between races from infection initiation to just prior to spore eruption.
Highlights
Wheat leaf rust can cause extensive economic impact on the wheat producing areas of the world, with significant yield losses reported during epidemics
MHDS and MLDS belong to North American lineage 3 (NA3; Tremblay et al, 2013) and were collected in 2004 in Kansas and Ohio, respectively
DIRECTIONS Secreted peptides of pathogenic fungi are of particular interest as some have been demonstrated to act as avirulence effectors in other studied systems (Dodds et al, 2004; De Wit et al, 2009; Nirmala et al, 2011)
Summary
Wheat leaf rust can cause extensive economic impact on the wheat producing areas of the world, with significant yield losses reported during epidemics. The causative agent of wheat leaf rust is Puccinia triticina (Pt) which is an obligate biotrophic basidiomycete (Bolton et al, 2008). Using thigmotrophic interactions with the surface of the leaf, the germ tube orients itself perpendicular to the leaf veins and grows until it reaches a stomata. The germ tube generates an appressorium over the stomata and penetrates the interior of the leaf. Communication between the growing fungus and the plant occurs across the haustorial membrane-plasma membrane interface in the form of proteins and other small molecules secreted by the fungus. The secreted proteins, some of which may be effectors, perform a variety of functions including host transcriptional reprogramming to benefit pathogen growth and mitigation of host defenses (Bolton et al, 2008)
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