Turn up the red: MADS-RIN-DIVARICATA1 module positively regulates carotenoid biosynthesis in nonclimacteric pepper fruits

Peppers are used worldwide for their nutritional value, unique taste, and vibrant colors. Unripe pepper fruits display shades such as white, purple, or green, transitioning to carotenoid-based colors—yellow, orange, and red—as they ripen. Carotenoids, lipid-soluble molecules essential for photosynthesis and photoprotection, are synthesized through well-characterized enzymes (Rodriguez-Uribe et al. 2012; Gómez-García and Ochoa-Alejo 2013), including phytoene synthase 1 (PSY1) and capsanthin/capsorubin synthase (CCS) (Fig.). The transcriptional network promoting carotenoid synthesis, among other traits, during ripening is partially elucidated in tomato, a model species for fruit ripening. However, as a nonclimacteric fruit, pepper relies on potentially different and less-understood regulatory mechanisms for carotenoid biosynthesis. Recently, the MYELOBLASTOSIS (MYB) containing two repeats (R2R3-MYB) transcription factor DIVARICATA1 was shown to be a positive regulator of capsanthin content through direct activation of PSY1 and CCS transcription (Song et al. 2023). Interestingly, the well-studied ripening regulator, MADS box transcription factor RIPENING INHIBITOR (MADS-RIN), key in triggering climacteric ripening, is coexpressed with DIVARICATA1 and activates its promoter in pepper. These findings open the question of whether these 2 transcription factors interact to modulate carotenoid biosynthesis (Song et al. 2023).