AaORA, a trichome-specific AP2/ERF transcription factor of Artemisia annua, is a positive regulator in the artemisinin biosynthetic pathway and in disease resistance to Botrytis cinerea

Abstract

· Six transcription factors of APETALA2/ethylene-response factor (AP2/ERF) family were cloned and analyzed in Artemisia annua. Real-time quantitative polymerase chain reaction (RT-Q-PCR) showed that AaORA exhibited similar expression patterns to those of amorpha-4,11-diene synthase gene (ADS), cytochrome P450-dependent hydroxylase gene (CYP71AV1) and double bond reductase 2 gene (DBR2) in different tissues of A. annua. · AaORA is a trichome-specific transcription factor, which is expressed in both glandular secretory trichomes (GSTs) and nonglandular T-shaped trichomes (TSTs) of A. annua. The result of subcellular localization shows that AaORA is targeted to the nuclei and the cytoplasm. · Overexpression and RNA interference (RNAi) of AaORA in A. annua regulated, positively and significantly, the expression levels of ADS, CYP71AV1, DBR2 and AaERF1. The up-regulated or down-regulated expression levels of these genes resulted in a significant increase or decrease in artemisinin and dihydroartemisinic acid. The results demonstrate that AaORA is a positive regulator in the biosynthesis of artemisinin. · Overexpression of AaORA in Arabidopsis thaliana increased greatly the transcript levels of the defense marker genes PLANT DEFENSIN1.2 (PDF1.2), HEVEIN-LIKE PROTEIN (HEL) and BASIC CHITINASE (B-CHI). After inoculation with Botrytis cinerea, the phenotypes of AaORA overexpression in A. thaliana and AaORA RNAi in A. annua demonstrate that AaORA is a positive regulator of disease resistance to B. cinerea.