Key Laboratory of Horticultural Plant Biology of MOE (Ministry of Education), Huazhong Agricultural University, Wuhan, Hubei 430070, China.
Department of Biological Sciences, Lehman College, The City University of New York, 250 Bedford Park Blvd. West, Bronx, New York 10468, USA.
Plant Physiol. 2021 Oct 5;187(2):829-845. doi: 10.1093/plphys/kiab291.
Domesticated citrus varieties are woody perennials and interspecific hybrid crops of global economic and nutritional importance. The citrus fruit "hesperidium" is a unique morphological innovation not found in any other plant lineage. Efforts to improve the nutritional quality of the fruit are predicated on understanding the underlying regulatory mechanisms responsible for fruit development, including temporal control of chlorophyll degradation and carotenoid biosynthesis. Here, we investigated the molecular basis of the navel orange (Citrus sinensis) brown flavedo mutation, which conditions flavedo that is brown instead of orange. To overcome the limitations of using traditional genetic approaches in citrus and other woody perennials, we developed a strategy to elucidate the underlying genetic lesion. We used a multi-omics approach to collect data from several genetic sources and plant chimeras to successfully decipher this mutation. The multi-omics strategy applied here will be valuable in driving future gene discovery efforts in citrus as well as in other woody perennial plants. The comparison of transcriptomic and genomic data from multiple genotypes and plant sectors revealed an underlying lesion in the gene encoding STAY-GREEN (SGR) protein, which simultaneously regulates carotenoid biosynthesis and chlorophyll degradation. However, unlike SGR of other plant species, we found that the carotenoid and chlorophyll regulatory activities could be uncoupled in the case of certain SGR alleles in citrus and thus we propose a model for the molecular mechanism underlying the brown flavedo phenotype. The economic and nutritional value of citrus makes these findings of wide interest. The strategy implemented, and the results obtained, constitute an advance for agro-industry by driving opportunities for citrus crop improvement.
栽培柑橘品种是具有经济和营养价值的木本多年生植物和种间杂种作物。柑橘类水果“桔柚”是一种独特的形态创新，在其他植物谱系中都没有发现。为了提高果实的营养价值，人们努力了解负责果实发育的潜在调控机制，包括叶绿素降解和类胡萝卜素生物合成的时间控制。在这里，我们研究了脐橙（Citrus sinensis）褐色果皮突变的分子基础，这种突变使果皮呈褐色而不是橙色。为了克服在柑橘和其他木本多年生植物中使用传统遗传方法的局限性，我们开发了一种阐明潜在遗传缺陷的策略。我们使用多组学方法从多个遗传来源和植物嵌合体收集数据，成功地破译了这个突变。这里应用的多组学策略将在推动柑橘以及其他木本多年生植物的未来基因发现工作中具有重要价值。来自多个基因型和植物部位的转录组和基因组数据的比较揭示了编码 STAY-GREEN（SGR）蛋白的基因中的一个潜在缺陷，该基因同时调节类胡萝卜素生物合成和叶绿素降解。然而，与其他植物物种的 SGR 不同，我们发现柑橘中某些 SGR 等位基因的类胡萝卜素和叶绿素调控活性可以解偶联，因此我们提出了一个分子机制模型，解释了褐色果皮表型的分子机制。柑橘的经济和营养价值使得这些发现具有广泛的兴趣。所实施的策略和获得的结果为农业产业提供了一个推动柑橘作物改良的机会，是一个进展。
