Chromoplasts are colored plastids that synthesize and store massive amounts of carotenoids. Chromoplast number and size define the sink strength for carotenoid accumulation in plants. However, nothing is known about the mechanisms controlling chromoplast number. Previously, a natural allele of Orange (OR), OR^His, was found to promote carotenoid accumulation by activating chromoplast differentiation and increasing carotenoid biosynthesis, but cells in orange tissues in melon fruit and cauliflower OR mutant have only one or two enlarged chromoplasts. In this study, we investigated an OR^His variant of Arabidopsis OR, genetically mimicking the melon OR^His allele, and found that it also constrains chromoplast number in Arabidopsis calli. Both in vitro and in vivo experiments demonstrate that OR^His specifically interacts with the Membrane Occupation and Recognition Nexus domain of ACCUMULATION AND REPLICATION OF CHLOROPLASTS 3 (ARC3), a crucial regulator of chloroplast division. We further showed that OR^His interferes with the interaction between ARC3 and PARALOG OF ARC6 (PARC6), another key regulator of chloroplast division, suggesting a role of OR^His in competing with PARC6 for binding to ARC3 to restrict chromoplast number. Overexpression or knockout of ARC3 in Arabidopsis OR^His plants significantly alters total carotenoid levels. Moreover, overexpression of the plastid division factor PLASTID DIVISION 1 greatly enhances carotenoid accumulation. These division factors likely alter carotenoid levels via their influence on chromoplast number and/or size. Taken together, our findings provide novel mechanistic insights into the machinery controlling chromoplast number and highlight a potential new strategy for enhancing carotenoid accumulation and nutritional value in food crops.

叶绿体是合成并存储大量类胡萝卜素的有色质体。叶绿体的数量和大小决定了植物中类胡萝卜素积累的吸收强度。然而，关于控制染色体质数的机制还一无所知。以前，人们发现橙子（OR）或OR ^His的天然等位基因通过激活色体的分化和增加类胡萝卜素的生物合成来促进类胡萝卜素的积累，但是瓜果和花椰菜OR突变体中橙色组织中的细胞只有一个或两个扩大的色体。在这项研究中，我们调查的或^他的变型拟南芥OR，遗传模仿瓜或^他的等位基因，发现它也限制了拟南芥愈伤组织中的染色体质数。二者在体外和在体内实验证明，OR^他专门与积累的膜职业与识别的Nexus域和复制叶绿体3（ARC3），叶绿体分裂的关键调节器交互。我们进一步表明，OR ^His 干扰了ARC3和ARC6的另一个参数（PARC6）之间的相互作用，PAR6是叶绿体分裂的另一个关键调节因子，表明OR ^His在与PARC6竞争与ARC3结合以限制染色体体数量方面发挥了作用。ARC3中的过表达或敲除拟南芥OR^他的植物显着改变了总类胡萝卜素水平。此外，质体分裂因子PLASTID DIVISION 1的过表达大大增强了类胡萝卜素的积累。这些分裂因子可能通过它们对色体数量和/或大小的影响而改变类胡萝卜素的水平。综上所述，我们的发现为控制色质体数量的机制提供了新颖的机械学见解，并突出了潜在的新策略，可增强食用作物中类胡萝卜素的积累和营养价值。