P-075 - The overexpression of the CsICS gene in sweet orange enhanced resistance to Candidatus Liberibacter asiaticus

Huanglongbing (HLB) is a devastating citrus disease caused by the bacterium Candidatus Liberibacter asiaticus (CLas), with no resistance described in commercial citrus genotypes. Genetically modified citrus plants aiming at HLB resistance or tolerance have been developed by overexpressing the CsICS (Citrus sinensis isochorismate synthase) gene. The ICS gene is involved in the biosynthesis of salicylic acid (SA) and potentially activates systemic acquired resistance to bacterial infections. Here, we challenged transgenic 'Hamlin' sweet orange plants with CLas and evaluated the expression of HLB symptoms. Fifteen replicates of each transgenic event and non-transgenic Hamlin plants were propagated and inoculated with CLas-infected buds 8 months after acclimatization. CLas detection started 6 months after inoculation (MAI), and evaluations were performed every 3 months until 30 MAI. The bacterial concentration was lower in the transgenic events CsICS 6-11 and 4-4 until 12 MAI. At 30 MAI, CLas concentrations obtained in the transgenic plants were similar to those of the control plants. However, CsICS 6-11 and 4-4 showed infection rates of 6.6% and 7.6%, respectively, at 30 MAI, whereas the wild-type plants exhibited 66% infection rate. Although the bacterium was detected at 12 MAI, no HLB symptoms were observed in plants from the CsICS 4-4 event. The overexpression of CsICS possibly activated the SA pathway response, preventing bacterial infection in these plants.