INDUCTION AND CONTROL OF CHROMOPLAST-SPECIFIC CAROTENOID GENES BY OXIDATIVE STRESS

The differentiation of chloroplasts into chromoplasts involves a serie s of biochemical changes that culminate with the intense accumulation of long chain chromophore carotenoids such as lycopene, rhodoxanthin, astaxanthin, anhydroeschsoltzxanthin, capsanthin, and capsorubin. The signal pathways mediating these transformations are unknown. Chromopla st carotenoids are known to accumulate in green tissues experiencing s tress conditions, and studies indicate that they provide efficient pro tection against oxidative stress. We tested the role of reactive oxyge n species (ROS) as regulators of chromoplast carotenoid biosynthesis i n vivo. The addition of ROS progenitors, such as menadione, tert-butyl hydroperoxide, or paraquat and prooxidants such as diamide or buthioni ne sulfoximine to green pericarp discs of pepper fruits rapidly and dr amatically induce the simultaneous expression of multiple carotenogeni c gene mRNAS that give rise to capsanthin. Similarly, down-regulation of catalase by amitrole induces expression of carotenogenic gene mRNAs leading to the synthesis of capsanthin in excised green pericarp disc s. ROS signals from plastids and mitochondria also contribute signific antly to this process. Analysis of the capsanthin-capsorubin synthase promoter in combination with a P-glucuronidase reporter gene reveals s trong activation in transformed pepper protoplasts challenged with the above ROS. Collectively these data demonstrate that ROS act as a nove l class of second messengers that mediate intense carotenoid synthesis during chromoplast differentiation.