Control of olive anthracnose through gene silencing and gene expression using a plant

Colletotrichum spp. is the causal agent of anthracnose in olive, a very common and severe disease in Portugal as well as in other Mediterranean countries. Symptoms typically occur on fruits as necrosis, leading to premature fruit drop or mummification, damaged fruits and poor oil quality. The Portuguese olive cultivar, Galega vulgar, is very susceptible to anthracnose. However, the disease can also severely affect less susceptible varieties under favorable environmental conditions, such as Arbequina and Picual, previously regarded as moderately resistant, and widely cultivated throughout Iberian Peninsula. 

The aim of this work is to develop a control measure against Colletotrichum spp. through RNA interference. RNAi is a mechanism that leads to post transcriptional gene silencing (PTGS). It occurs when double-stranded RNA (dsRNA) molecules are recognized by an organism as foreign, triggering a process in which dsRNA is degraded into ca. 21-24 nt small interfering RNAs (siRNAs) which can then guide an RNase complex to specifically target homologous RNAs, preventing gene expression. This work plan relies on the triggering of Colletotrichum spp. silencing mechanism through VIGS. Virus induced gene silencing (VIGS) allows specific silencing of foreign genes that can be inserted in an optimized virus vector and then inoculated in plants. When a dsRNA sequence of a gene essential for the fungi survival is introduced into a plant through a virus vector, and the fungi “feeds” on that plant, it ingests the plant cytoplasm and acquires the dsRNA; RNAi will be triggered, homologous RNAs will be targeted, the expression of that fungi gene will be prevented and fungi will be destroyed. 

The OMMV, OLV 1 and TNV-D clones will be used to verify their ability to infect the Colletotrichum spp. These three viruses have characteristics that place them as very promising vector tools. Their small genome makes them easy to manipulate, in addition, they are symptomless or cause only mild systemic symptoms in a wide range of crops, which will ease their manipulation into symptomless constructs, and allow their application to a high number of plants. To our knowledge no studies have been done concerning this matter using these small necroviruses. Finally, the created vector will act as a VIGS, capable of replicating in plants and inside fungus, and carrying specific RNA sequences, which will trigger RNAi silencing in Colletotrichum spp. and contribute to the efficient control of the fungus. 

This will give to the plant a significant advantage in its protection against a infection of that fungus. This work plan has a significant interest because no tool like the one that will be developed here are available for plant disease management, leaving eradication or prevention through sanitary measures. Until date, the best control strategy for this fungal disease relies on synthetic fungicides that are unspecific, inefficient, expensive and harmful to the environment.