Phylloxera genome that took over European vineyards in the 19th century, deciphered

The study, published in the journal BMC Biology, affirms the plague comes from North America and likely from wild populations located over the upper course of the Mississippi River. The conclusions of the study helped to reconstruct the biological invasion that unchained mortal plagues on the European vineyards in the 19^th century and to advance in the strategies to improve the productivity in viticulture.

The sequencing of the new genome has been promoted by the international consortium -more than seventy experts from eight countries worldwide- created in 2011 and led by the French National Research Institute for Agriculture (INRAE). The study counts on the technical support of the INRAE-BIPAA platform, which enabled the access to genomic resources on insects associated with agricultural ecosystems.

The experts Silvia Hinojosa-Alvarez, Jose F. Sánchez-Herrero, Paula Escuer and Pablo Librado take part in the UB-IRBio team as well. The team focused its scientific contribution in the genomic annotation and analysis of several families of genes of the olfactory system of the phylloxera. The general study, led by researchers François Delmotte and Denis Tagu (INRAE), counts on the participation of the experts from the Centre for Genomic Regulation (CRG) and UPF, apart from the Science Park of the University of Valencia. 

Phylloxera: from Mississippi riverbanks to the French vineyards

The grape phylloxera (Daktulosphaira vitifoliae) is a hemipteran insect from the family Phylloxeridae, which feeds from the sap of the roots in the vineyards. Described for the first time in 1854 by the entomologist Asa Fitch in the United States, which originated the first infection outbreaks in France in 1863 until it was identified in 1868 by Bazille, Planchon and Sahut, members of the Chambre dʼAgriculture de lʼHérault in Montpellier.

The intense trade of vines between the United States and Europe could have been the open doors for the insect, which spread widely around France -the most affected country by this plague-, and other European areas. 

A new genic family with more than 2,700 genes

The DNA nuclear genomic analyses of the phylloxera reveal the existence of the largest genic family ever identified with a genome -with about 2,700 genes, when the average does not go over 200-, which would account for a 10% of the genome of this insect.

Researchers believe these genes are essential for the interaction between the phylloxera and the vineyard: they code the small secreted proteins -known as effectors- that could take part in the deactivation of the basic defenses of the plant. In the region of origin, the coevolution between the plant and the plague could have enabled the vineyards to be resistant to the insect. However, the vineyards in Europe did not have such a defense system to fight the threat of the new plague and the effectors.

The study has worked on sample campaigns of the plague in Europe and the United States, and it affirms the phylloxera that invaded Europe comes from the species Vitis riparia, a wild type from American vineyards. “As expected, the study reveals there is a great genetic variability among the native species of D. vitifoliae compared to the European strains. In particular, the comparison of these patterns of genetic variability is what enabled researchers to trace the geographical routes of the biological invasion”, note the experts Julio Rozas and Alejandro Sánchez-Gracia, heads of the Research Group on Evolutionary Genomics and Bioinformatics UB-IRBio. 

From basic research to an improvement of wine production

Promoting knowledge on basic research is the most direct ccontribution of the studies that finish with genomic sequencing of a new species. “These new findings provide many biological information and basic knowledge on the evolution of insects -specially the aphids-, and about the genetics and selection of roots of those phylloxera-resistant plants”, notes Professor Julio Rozas.

From an applied field, the genomic data of the new study will enable the promotion of genetic improvement in the practice of viticulture. Therefore, a better knowledge of the evolution and action mechanisms of the new family of effector genes will help design strategies to block the action through interventions on the plant or the parasite.

“The new study is an advance in our understanding of biological invasions and the potentially disastrous consequences on agriculture, and therefore, on the important social and economic sectors”, notes researcher Alejandro Sánchez-Gracia.

Decipgering the genome of living beings

The Research Group on Evolutionary Genomics and Bioinformatics UB-IRBio has a significative experience in international studies which allowed them to decipher the genome of several organisms of scientific interest. Therefore, they are the co-authors of the genetic sequencing of the genome of the spider Dysdera sylvatica Schmidt 1981 -an endemic species of the Canary Island forests- (GigaScience, 2019); the plant varieties of the avocado Persea Americana var. drymifolia and Persea Americana Mill. Cv. Hass (Proceedings of the National Academy of Science, 2019); the tick Ixodes scapular, of great interest in public and veterinary health (Nature Communications, 2016); the myriapod Strigamia maritima, a common centipede in the coasts of northern Europe (PLOS Biology, 2014), and the coffee plant Coffea canephora (Science, 2014). 

In the field of insect genomics, they also took part in the decipherment of the pea aphid genome (Acyrthosiphon pisum),  -a parasite of legume plants that causes serious agricultural plagues-, published in the journal PLoS Biology  in 2010 by an international consortium that gave way to the scientific platform to decipher the genome of the phylloxera.