Miquel Barberà (left) and David Martínez

The genome of phylloxera, an insect that caused pests until it devastated European vineyards in the 19th century, has been deciphered by an international team in which researchers Miquel Barberà and David Martínez, from the Institute of Integrative Systems Biology (I2SysBio), a center of the University of Valencia and the CSIC, participate. The study is published in the journal BMC Biology.

The work confirms that the plague comes from North America and most likely from wild populations located along the upper reaches of the Mississippi River. The conclusions of the study have helped to reconstruct the biological invasion that unleashed the deadly pests on European vineyards in the 19th century, as well as to advance strategies to improve productivity in viticulture.

The sequencing of the new genome has been promoted by the international consortium – more than seventy experts from eight countries around the world – created in 2011 and led by the National Institute of Agriculture (INRAE) of France. The work also has technical support from the INRAE-BIPAA platform, which has facilitated access to genomic resources on insects associated with agroecosystems. The study also has the participation of scientists from the IRBio Biodiversity Research Institute (University of Barcelona), the Center for Genomic Regulation (CRG) of Catalonia and the Pompeu Fabra University.

The work of the I²SysBio experts has focused on the annotation of a series of genes related to the circadian rhythm –a type of biorhythm– and with the induction of the sexual phase. “These are genes involved in photoreception, as well as candidate genes to trigger an appropriate response to certain environmental changes that produce modifications in the life cycle,” details David Martínez, researcher at the I²SysBio and one of the signatories of the article. Both Martínez and Miquel Barberà have dedicated the last few years of research to identifying and characterizing genes related to the biological cycle of aphids, and ten years ago they contributed to the sequencing and publication of the genome of Acyrthosiphon pisum. Hence the participation of the I²SysBio researchers in the deciphering of the phylloxera genome.

Phyloxera: from the banks of the Mississippi to the French vineyards

Phylloxera (Daktulosphaira vitifoliae) is an insect Hemipteran of the phylloxeridae family that feeds on the sap obtained from the roots of the vines. Described for the first time in 1854 by the entomologist Asa Fitch in the United States, it caused the first outbreaks of infection in France in 1863 until it was definitively identified in 1868 by Bazille, Planchon and Sahut, members of the Hérault Agricultural Society in Montpellier.

The intense trade in vines between the United States and Europe could have been the accidental gateway of the insect, which spread inexorably throughout France – the country most affected by the plague – and through other European territories.

A new gene family with more than 2,700 genes

Analyses of the genomic sequence of the nuclear DNA of phylloxera reveal the existence of the largest gene family ever identified in a genome – with about 2,700 genes when they rarely exceed 200 – which would represent 10% of the insect's genome.

These genes, probably essential for the interactions between phylloxera and the vineyard, encode small secreted proteins – known as effectors – that could intervene in the deactivation of the plant's basic defenses. In the vineyards of the region of origin, the coevolution between plant and pest would have allowed the vines to resist the insect. On the other hand, the vines grown in Europe did not have a defense system adapted to ward off the threat of the new pest and its lethal cocktail of effectors.

The published work also confirms that the phylloxera that invaded Europe comes from the species Vitis riparia, a wild type of American vineyard.

From basic research to improving production viticulture

From an applied perspective, the genomic information from the new study will make it possible to enhance genetic improvement in the practice of viticulture. Thus, a better knowledge of the evolution and mechanisms of action of the new family of effector genes will help to design strategies that block their action through interventions on the plant or the parasite.

List of links:

• Article to BMC Biology