Abstract
Jasmonic acid (JA) plays a crucial role in various biological processes including development, signal transduction and stress response. Allene oxide synthase (AOS) catalyzing (13S)-hydroperoxyoctadecatrienoic acid (13-HPOT) to an unstable allene oxide is involved in the first step of JA biosynthesis. Here, we isolated the PtAOS1 gene and its promoter from trifoliate orange (Poncirus trifoliata). PtAOS1 contains a putative chloroplast targeting sequence in N-terminal and shows relative to pistachio (Pistacia vera) AOS. A number of stress-, light- and hormone-related cis-elements were found in the PtAOS1 promoter which may be responsible for the up-regulation of PtAOS1 under drought and JA treatments. Transient expression in tobacco (Nicotiana benthamiana) demonstrated that the P−532 (−532 to +1) fragment conferring drive activity was a core region in the PtAOS1 promoter. Using yeast one-hybrid, three novel proteins, PtDUF886, PtDUF1685 and PtRAP2.4, binding to P−532 were identified. The dual luciferase assay in tobacco illustrated that all three transcription factors could enhance PtAOS1 promoter activity. Genes PtDUF1685 and PtRAP2.4 shared an expression pattern which was induced significantly by drought stress. These findings should be available evidence for trifoliate orange responding to drought through JA modulation.
Highlights
In the south of China, seasonal drought happening from July to September generally damages the citrus industry regularly
Over-expression of cabbage BaAOS in Arabidopsis increased basal Jasmonic acid (JA) levels compared with wild type: with drought stress, transgenic lines exhibited a drastic increase in endogenous JA and higher tolerance [7]
G-box: cis-acting regulatory element involved in light responsiveness; GA-motif: part of a light responsive element; GT1-motif: light responsive element; MBS: MYB binding Site; MNF1: light responsive element; MRE: MYB binding site involved in light responsiveness; Skn-1_motif: cis-acting regulatory element required for endosperm expression; Sp1: light responsive element; TATA-box: core promoter element around −30 of transcription start; TC-rich repeats: cis-acting element involved in defense and stress responsiveness; TCA-element: cis-acting element involved in salicylic acid responsiveness
Summary
In the south of China, seasonal drought happening from July to September generally damages the citrus industry regularly. Trifoliate orange (Poncirus trifoliata) is the main citrus rootstock in China because of its excellent tolerance or resistance to stresses including drought. JAs play positive roles in plants’ abiotic stress response. Previous studies demonstrated JA or MeJA could modulate plant physiological responses to abiotic stress. In a JA-deficient tomato, activity decreases in antioxidants accelerated oxidative stress by salt treatment, indicating that endogenous JA might play a positive role in plant salt tolerance [15]. AOS was found acting a positive role in plant drought tolerance. Over-expression of cabbage BaAOS in Arabidopsis increased basal JA levels compared with wild type: with drought stress, transgenic lines exhibited a drastic increase in endogenous JA and higher tolerance [7]. Responses of PtDUF886, PtDUF1685 and PtRAP2.4 to drought stress were investigated further
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