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Plant pathogens increase their own transmission

Recent research has found that viruses infect plants (viral hosts) and render them attractive to insects (viral vectors) thereby potentially facilitating viral transmission. An EU project is investigating the intricacies of the complex relationships between plants, their viruses, and disease carriers or vectors.
Plant pathogens increase their own transmission
Plant pathogens, in particular viruses, can manipulate their hosts' biochemistry to attract insect vectors to transmit the virus to other plants. Although beneficial for pathogen transmission, little is known about this adaptive feature, its function and associated factors involved in survival in multiple infections.

The 'Evolution of plant volatiles manipulation by vectored pathogens' (PLANT VOLATILES) aimed to fill this gap. The researchers started by investigating the mechanisms in play when the tomato yellow leaf curl China virus (TYLCCNV), transmitted by whitefly, infects the model plant Arabidopsis thaliana or thale cress.

PLANT VOLATILES members found that a viral gene, beta-C1, alters the expression of jasmonic acid, a defence chemical against whitefly. Moreover, infected Arabidopsis produces more linalool, a volatile compound attractive to insect vectors. Results show that plant modification is down to a single gene and is not due to viral multiplication in host tissues. Beta-C1 is also responsible for core regulation mechanisms, a fact that is in line with the size-constrained virus — the gene has multiple functions.

Competition between pathogens, a more ecological aspect of virus-induced changes, was then investigated. This time, watermelon mosaic virus (WMV) and zucchini yellow mosaic virus (ZYMV) became infecting competitors. The changes in co-infected plants were the same as the singly infected ZYMV plant. This suggests that host–phenotype manipulators are vulnerable to cheating by competitors that can't themselves change their plant hosts biochemically.

Additionally, the team investigated the effects of viral infection in members of the cucurbit family (e.g. squashes and cucumbers) on their susceptibility to the often-fatal bacterium Erwinia tracheiphila. An early infection with ZYMV only slightly reduced effects on symptoms and plant death, suggesting that this is due to reduced visits by the beetle vector involved. PLANT VOLATILES research has significant implications for understanding pathogen evolution. Applied, there could be benefits in the agricultural and horticultural sectors as insect vectors play a major role in disease transmission.

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