Selection and evaluation of citrus phloem specific promoters

Background The citrus industry worldwide has faced major economic losses due to the occurrence of Huanglongbing (HLB), a disease caused by Candidatus Liberibacter spp., Gramnegative bacteria restricted to the phloem of their hosts. Due to the lack of commercial varieties that could resist to these bacteria, genetic transformation comes as an important alternative for improving these varieties and managing the disease. Most of the work with citrus genetic transformation uses constitutive promoters, but recently studies have intensified the search for tissue-specific promoters, making possible to direct the transgene expression to the phloem and reduce it in other undesired parts of the plant, such as the fruits. It is possible that tissue-specific promoter sequences obtained from the same plant species have better acceptance by the customers and this was the objective of our work: prospect phloem-specific promoters from the citrus genome that can be used for citrus transformation with the objective to deliver transgene expression directly to the tissue of Ca. Liberibacter spp. accumulation.