RNAi-based enhanced resistance to Cowpea severe mosaic virus and Cowpea aphid-borne mosaic virus in transgenic cowpea

Cowpea (Vigna unguiculata) is one of the most important legumes cultivated in many parts of the world. The diseases caused by Cowpea severe mosaic virus (CPSMV) and Cowpea aphid-borne mosaic virus (CABMV) are considered among the most important constraints on yield and quality, especially in Latin America and Africa. Here, the concept of using an RNA interference construct to silence the CPSMV proteinase cofactor gene and the CABMV coat protein gene is explored, in order to generate resistant transgenic cowpea plants. Ten cowpea transgenic lines were produced, presenting a normal phenotype and transferring the transgene to the next generation. Plants were tested for resistance to both CABMV and CPSMV by mechanical co-inoculation. Seven lines presented milder symptoms when compared to the control and three lines presented enhanced resistance to both viruses. Northern analyses were carried out to detect the transgene-derived small interfering RNA (siRNA) in leaves and revealed no correlation between siRNA levels and virus resistance. Additionally, in the symptomless resistant lines the resistance was homozygosis-dependent. Only homozygous plants remained uninfected while hemizygous plants presented milder symptoms.