Abstract
BackgroundLeaf rust, which is caused by the fungus Hemileia vastatrix (Pucciniales), is a devastating disease that affects coffee plants (Coffea arabica L.). Disadvantages that are associated with currently developed phytoprotection approaches have recently led to the search for alternative strategies. These include genetic manipulations that constitutively activate disease resistance signaling pathways. However, molecular actors of such pathways still remain unknown in C. arabica. In this study, we have isolated and characterized the coffee NDR1 gene, whose Arabidopsis ortholog is a well-known master regulator of the hypersensitive response that is dependent on coiled-coil type R-proteins.ResultsTwo highly homologous cDNAs coding for putative NDR1 proteins were identified and cloned from leaves of coffee plants. One of the candidate coding sequences was then expressed in the Arabidopsis knock-out null mutant ndr1-1. Upon a challenge with a specific strain of the bacterium Pseudomonas syringae (DC3000::AvrRpt2), analysis of both macroscopic symptoms and in planta microbial growth showed that the coffee cDNA was able to restore the resistance phenotype in the mutant genetic background. Thus, the cDNA was dubbed CaNDR1a (standing for Coffea arabica Non-race specific Disease Resistance 1a). Finally, biochemical and microscopy data were obtained that strongly suggest the mechanistic conservation of the NDR1-driven function within coffee and Arabidopsis plants. Using a transient expression system, it was indeed shown that the CaNDR1a protein, like its Arabidopsis counterpart, is localized to the plasma membrane, where it is possibly tethered by means of a GPI anchor.ConclusionsOur data provide molecular and genetic evidence for the identification of a novel functional NDR1 homolog in plants. As a key regulator initiating hypersensitive signalling pathways, CaNDR1 gene(s) might be target(s) of choice for manipulating the coffee innate immune system and achieving broad spectrum resistance to pathogens. Given the potential conservation of NDR1-dependent defense mechanisms between Arabidopsis and coffee plants, our work also suggests new ways to isolate the as-yet-unidentified R-gene(s) responsible for resistance to H. vastatrix.
Highlights
Leaf rust, which is caused by the fungus Hemileia vastatrix (Pucciniales), is a devastating disease that affects coffee plants (Coffea arabica L.)
Cloning and analysis of a novel NON-RACE-SPECIFIC DISEASE RESISTANCE 1 (NDR1) sequence homolog from Coffea arabica In previous work [19], we used a subtractive hybridization approach to identify genes involved in defense/resistance of coffee plants (C. arabica L.) to the orange rust fungus H. vastatrix
Of the 9 Expressed Sequence Tags (ESTs) which were significantly up-regulated during HR, one displayed 43% identity with the canonical NDR1 coding sequence from A. thaliana
Summary
Leaf rust, which is caused by the fungus Hemileia vastatrix (Pucciniales), is a devastating disease that affects coffee plants (Coffea arabica L.). Disadvantages that are associated with currently developed phytoprotection approaches have recently led to the search for alternative strategies. These include genetic manipulations that constitutively activate disease resistance signaling pathways. It is commonly accepted that the outcome of coffee/rust interactions, whether the plant resists pathogen attack (incompatibility) or develops disease (compatibility), relies on the gene-for-gene model [9], which has been recently amended [10]. Virulent rust races are believed to secrete effectors that escape or even counteract the host surveillance system, which allow for the highjacking of coffee cell metabolism and tissue colonization [11]
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