Centro de Biología Molecular Vegetal, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
Centre for Research in Agricultural Genomics (CRAG), CSIC-IRTA-UAB-UB, Barcelona, Spain.
Plant Physiol. 2022 Jun 27;189(3):1450-1465. doi: 10.1093/plphys/kiac097.
Light stimulates carotenoid synthesis in plants during photomorphogenesis through the expression of PHYTOENE SYNTHASE (PSY), a key gene in carotenoid biosynthesis. The orange carrot (Daucus carota) synthesizes and accumulates high amounts of carotenoids in the taproot that grows underground. Contrary to other organs, light impairs carrot taproot development and represses the expression of carotenogenic genes, such as DcPSY1 and DcPSY2, reducing carotenoid accumulation. By means of RNA sequencing, in a previous analysis, we observed that carrot PHYTOCHROME RAPIDLY REGULATED1 (DcPAR1) is more highly expressed in the underground grown taproot compared with those grown in light. PAR1 is a transcriptional cofactor with a negative role in shade avoidance syndrome regulation in Arabidopsis (Arabidopsis thaliana) through the dimerization with PHYTOCHROME-INTERACTING FACTORs (PIFs), allowing a moderate synthesis of carotenoids. Here, we show that overexpressing AtPAR1 in carrot increases carotenoid production in taproots grown underground as well as DcPSY1 expression. The high expression of AtPAR1 and DcPAR1 led us to hypothesize a functional role of DcPAR1 that was verified through in vivo binding to AtPIF7 and overexpression in Arabidopsis, where AtPSY expression and carotenoid accumulation increased together with a photomorphogenic phenotype. Finally, DcPAR1 antisense carrot lines presented a dramatic decrease in carotenoid levels and in relative expression of key carotenogenic genes as well as impaired taproot development. These results suggest that DcPAR1 is a key factor for secondary root development and carotenoid synthesis in carrot taproot grown underground.
在光形态发生过程中，光通过表达类胡萝卜素生物合成的关键基因——八氢番茄红素合酶（PSY）来刺激植物中类胡萝卜素的合成。橙色胡萝卜（Daucus carota）在地下生长的主根中合成并积累大量类胡萝卜素。与其他器官相反，光会损害胡萝卜主根的发育，并抑制类胡萝卜素生物合成基因（如 DcPSY1 和 DcPSY2）的表达，从而减少类胡萝卜素的积累。在之前的分析中，通过 RNA 测序，我们观察到胡萝卜光形态建成快速调控 1 型（DcPAR1）在地下生长的主根中的表达量高于在光下生长的主根。PAR1 是一种转录共激活因子，通过与光受体互作因子（PIFs）二聚化，在拟南芥的避阴反应调节中发挥负作用，从而适度合成类胡萝卜素。在这里，我们证明在胡萝卜中过表达 AtPAR1 会增加地下生长的主根中的类胡萝卜素产量，并提高 DcPSY1 的表达。AtPAR1 和 DcPAR1 的高表达使我们假设 DcPAR1 具有功能作用，这通过体内与 AtPIF7 的结合和在拟南芥中的过表达得到了验证，在拟南芥中，AtPSY 的表达和类胡萝卜素的积累与光形态建成表型一起增加。最后，DcPAR1 反义胡萝卜系的类胡萝卜素水平和关键类胡萝卜素生物合成基因的相对表达显著降低，主根发育受损。这些结果表明，DcPAR1 是地下生长的胡萝卜主根次生根发育和类胡萝卜素合成的关键因素。
