Overview of the functional virulent genome of the coffee leaf rust pathogen Hemileia vastatrix with an emphasis on early stages of infection

Abstract

Hemileia vastatrix is the causal agent of coffee leaf rust, the most important disease of coffee Arabica. In this work, a 454-pyrosequencing transcriptome analysis of H. vastatrix germinating urediniospores (gU) and appressoria (Ap) was performed and compared to previously published in planta haustoria-rich (H) data. A total of 9234 transcripts were identified and annotated. Ca. 50% of these transcripts showed no significant homology to international databases. Only 784 sequences were shared by the three conditions, and 75% were exclusive of either gU (2146), Ap (1479) or H (3270). Relative transcript abundance and RT-qPCR analyses for a selection of genes indicated a particularly active metabolism, translational activity and production of new structures in the appressoria and intense signaling, transport, secretory activity and cellular multiplication in the germinating urediniospores, suggesting the onset of a plant-fungus dialogue as early as at the germ tube stage. Gene expression related to the production of carbohydrate-active enzymes and accumulation of glycerol in germinating urediniospores and appressoria suggests that combined lytic and physical mechanisms are involved in appressoria-mediated penetration. Besides contributing to the characterization of molecular processes leading to appressoria-mediated infection by rust fungi, these results point toward the identification of new H. vastatrix candidate virulence factors, with 516 genes predicted to encode secreted proteins.

The Hemileia vastatrix effector HvEC‐016 suppresses bacterial blight symptoms in coffee genotypes with the SH1 rust resistance gene

“…The S H 1 gene has not yet been cloned and thus, conventional transient coexpression assays in other plant species, such as Nicotiana benthamiana , are not possible at the moment. Notably, H. vastatrix isolate 178a (race XIV), which is also avirulent on S H 1 plants, carries the same allele of HvEC‐016 as that of isolate Hv‐01 (race II) (Fernandez et al ., ; Talhinhas et al ., ). Also, consistent with the expression profile observed in our study, HvEC‐016 was identified in all three libraries of isolate 178a (interaction, appressoria and germinating urediniospores) screened by these authors.…”

“…Here we report a total of 94 Hemileia ‐specific candidate effector genes, referred to as HvEC s, of which 14 have not been reported previously. We provide for 34 earlier partial effectors full‐length sequences, and confirm 46 effector sequences already published (Fernandez et al ., ; Cristancho et al ., ; Talhinhas et al ., ). We identified genes encoding proteins with significant similarity to the previously reported RTP1 (Kemen et al ., ; Vieira et al ., ; Pretsch et al ., ) and HESP proteins (Dodds et al ., ; Barrett et al ., ) in the H. vastatrix secretome, providing validation for our prediction.…”

“…Recently, at least 500 putative H. vastatrix secreted proteins were predicted using bioinformatics pipelines (Fernandez et al ., ; Cristancho et al ., ; Talhinhas et al ., ). In this predicted secretome, the authors identified proteins showing similarity to haustorially expressed secreted proteins (HESPs) from the flax rust fungus Melampsora lini (Catanzariti et al ., ), and to the bean rust transferred protein 1 (RTP1), found previously in other rust fungi (Kemen et al ., ; Vieira et al ., ; Pretsch et al ., ).…”

Advances in understanding obligate biotrophy in rust fungi

“…Dikaryotic aeciospores and urediniospores enter the host leaf through openings in the stomata, after appressorium differentiation (Voegele et al, 2009). Several transcriptomic analyses of appressoria formation of urediniospores led to identification of the genes responsible for metabolism and regulation of the cell division cycle, indicating that this structure plays an active role in the penetration process (Hu et al, 2007;Stone et al, 2012;Talhinhas et al, 2014). Urediniospores from the soybean rust fungus directly penetrate their host through the epidermis, in a similar manner to basidiospores of heteroecious fungi, and form an appressorium with a high cell turgor pressure of 5.13 MPa (Loehrer et al, 2014a), which correlates with what has been observed in other fungal plant pathogens (Ryder & Talbot, 2015).…”

“…Hundreds of candidate effectors have been identified in H. vastatrix by genomic and transcriptomic approaches (Fernandez et al, 2012;Cristancho et al, 2014;Talhinhas et al, 2014). Similar to effectoromic screens conducted in P. graminis f. sp.…”