Isolation and expression analysis of four putative structural genes involved in anthocyanin biosynthesis in Begonia semperflorens

As the major colour pigments in plants, anthocyanins play a positive photoprotective role in plant resistance to abiotic stress. In this work, variations in anthocyanin concentration were determined in the leaves of Begonia semperflorens growing under high light (HL; 900 mu mol m(-2) s(-1)) or low temperature (LT; 15 degrees C day/6 degrees C night) conditions. Partial cDNA sequences of four structural genes associated with the biosynthesis of anthocyanins were isolated from leaves. These genes encoded phenylalanine ammonia-lyase (BsPAL), chalcone synthase (BsCHS), flavonone-3-hydroxylase (BsF3H), and anthocyanidin synthase (BsANS). The patterns of expression of these genes after HL or LT treatment were investigated using real-time reverse transcription-quantitative PCR (RT-qPCR). Anthocyanins, which remained at low concentrations in untreated leaves, increased significantly after HL or LT treatment. Transcript levels of all four genes corresponded, in general, with these changing patterns, but their expression profiles were significantly different between the HL and LT treatments. After LT treatment, the expression of BsPAL and BsF3H increased significantly in the first 2 d, then decreased, while transcript levels of BsCHS and BsANS increased gradually and reached their maximum level by day-6. During HL treatment, the expression of BsCHS and BsF3H responded almost immediately 0.5 d after treatment, then BsF3H expression decreased sharply to a level only slightly higher than in the untreated controls. However, expression of BsCHS remained at high levels. Expression of BsANS increased sharply 1 d after HL treatment, then decreased until day-4. Transcription of BsPAL increased rapidly 2 d after treatment, then decreased rapidly. Understanding the different regulatory mechanisms of anthocyanin biosynthesis under HL or LT stress would improve our understanding of the genetic and physiological mechanisms of adaption of B. semperflorens to abiotic stresses.