Modulation of the transcriptional activity of the AP2/ERF family (DREB genes) in orange (Citrus sinensis) leaves subjected to drought stress

Ethylene response factor (ERF) play important role in the development and expression of genes that regulate plant response to biotic and abiotic stresses. In this study, six Citrus sinensis genes belonging to AP2/ERF family, dehydration-responsive element-binding protein (DREB) genes, (CitsERF01 to CitsERF06) were identified and five of them had their expression pattern evaluated in leaves of 18 month-seedling orange (C. sinensis) subjected to increasing intervals of drought stress. Two gene transcription patterns were identified. In the first pattern, transcription of CitsERF01 and CitsERF03 genes was delayed for many days and did not occur until the 12th day. In the second pattern, transcription of CitsERF04, CitsERF05 and CitsERF06 was immediate, and their relative value increased steadily, also reaching its peak at the 12th day. However, in both cases, transcription of CitsERF genes was down regulated with water recovery. These patterns suggest that CitsERFs genes may be involved in regulation mechanisms of drought response of C. sinensis and are controlled by factors acting in cascade. The data from this study will help understand the genetic mechanisms of drought tolerance, which could contribute to breeding programs of orange.  Key words: Gene expression, transcript factor; dehydration-responsive element-binding protein genes, semi-quantitative analysis RT-PCR