"Cucumber mosaic virus (CMV) is one of the two most important viruses of field-grown and glasshouse crops in the EU and worldwide, causing considerable losses annually. Moreover CMV attacks more crop and wild-plant species than any other virus. A key contributor to the success of CMV is a recently-discovered factor made by the virus: the 2b protein. Until recently the most important known role for the 2b protein was that it counterattacks resistance mechanisms that plants use to defend against virus infection. In particular, the 2b protein can disrupt a form of antiviral resistance that is controlled by a variety of small RNAs (small interfering and microRNAs). We have discovered a remarkable and novel property of the 2b protein: it inhibits plant resistance to insects. This is very important because under natural conditions, CMV (like most plant viruses) is transmitted from plant to plant by aphids. Aphids are insects that feed on plants and in doing so promote the spread of disease caused by viruses and other disease-causing organisms. We can imagine that it will be in the interests of the virus to inhibit defences against insects so that sufficient aphids will settle on CMV-infected plants to pass on the infection to new host plants. We found that the 2b protein blocks the action of a natural chemical signal, jasmonic acid, which stimulates anti-insect defences in plants. We also discovered that in plants infected with a mutant strain of CMV, called CMVΔ2b, that is unable to make the 2b protein, these defences are activated. We will identify novel, potentially insecticidal gene products and low molecular weight chemicals induced by infection with CMVΔ2b. In addition, we will determine if inhibition of jasmonic acid-induced resistance to aphids is a property common to 2b proteins from strains belonging to all three subgroups of CMV and further elucidate the role of small RNAs in the regulation of jasmonic acid-mediated resistance to aphids."