Chayut Noam, Yuan Hui, Saar Yuval, Zheng Yi, Sun Tianhu, Zhou Xuesong, Hermanns Anna, Oren Elad, Faigenboim Adi, Hui Maixia, Fei Zhangjun, Mazourek Michael, Burger Joseph, Tadmor Yaakov, Li Li
Department of Vegetable Research, ARO, Newe Ya'ar Research Center, P.O. Box 1021, Ramat Yishay, 30095, Israel.
John Innes Centre, Norwich Research Park, Norwich, UK.
Hortic Res. 2021 May 1;8(1):112. doi: 10.1038/s41438-021-00547-6.
Carotenoids, such as β-carotene, accumulate in chromoplasts of various fleshy fruits, awarding them with colors, aromas, and nutrients. The Orange (CmOr) gene controls β-carotene accumulation in melon fruit by posttranslationally enhancing carotenogenesis and repressing β-carotene turnover in chromoplasts. Carotenoid isomerase (CRTISO) isomerizes yellow prolycopene into red lycopene, a prerequisite for further metabolism into β-carotene. We comparatively analyzed the developing fruit transcriptomes of orange-colored melon and its two isogenic EMS-induced mutants, low-β (Cmor) and yofi (Cmcrtiso). The Cmor mutation in low-β caused a major transcriptomic change in the mature fruit. In contrast, the Cmcrtiso mutation in yofi significantly changed the transcriptome only in early fruit developmental stages. These findings indicate that melon fruit transcriptome is primarily altered by changes in carotenoid metabolic flux and plastid conversion, but minimally by carotenoid composition in the ripe fruit. Clustering of the differentially expressed genes into functional groups revealed an association between fruit carotenoid metabolic flux with the maintenance of the photosynthetic apparatus in fruit chloroplasts. Moreover, large numbers of thylakoid localized photosynthetic genes were differentially expressed in low-β. CmOR family proteins were found to physically interact with light-harvesting chlorophyll a-b binding proteins, suggesting a new role of CmOR for chloroplast maintenance in melon fruit. This study brings more insights into the cellular and metabolic processes associated with fruit carotenoid accumulation in melon fruit and reveals a new maintenance mechanism of the photosynthetic apparatus for plastid development.
类胡萝卜素，如β-胡萝卜素，积累在各种肉质果实的有色体中，赋予果实颜色、香气和营养。橙色（CmOr）基因通过翻译后增强类胡萝卜素生成并抑制有色体中β-胡萝卜素的周转来控制甜瓜果实中β-胡萝卜素的积累。类胡萝卜素异构酶（CRTISO）将黄色原番茄红素异构化为红色番茄红素，这是进一步代谢为β-胡萝卜素的前提条件。我们比较分析了橙色甜瓜及其两个由甲基磺酸乙酯（EMS）诱变产生的同基因突变体低β（Cmor）和yofi（Cmcrtiso）发育中的果实转录组。低β突变体中的Cmor突变导致成熟果实发生重大转录组变化。相比之下，yofi突变体中的Cmcrtiso突变仅在果实发育早期显著改变了转录组。这些发现表明，甜瓜果实转录组主要受类胡萝卜素代谢通量和质体转化变化的影响，而受成熟果实中类胡萝卜素组成的影响最小。将差异表达基因聚类到功能组中，揭示了果实类胡萝卜素代谢通量与果实叶绿体中光合装置维持之间的关联。此外，大量定位于类囊体的光合基因在低β突变体中差异表达。发现CmOR家族蛋白与捕光叶绿素a-b结合蛋白发生物理相互作用，这表明CmOR在甜瓜果实叶绿体维持中具有新作用。本研究为甜瓜果实中与类胡萝卜素积累相关的细胞和代谢过程提供了更多见解，并揭示了光合装置对质体发育的一种新的维持机制。
