近日，華中農(nóng)業(yè)大學(xué)園藝林學(xué)學(xué)院園藝植物生物學(xué)教育部重點(diǎn)實(shí)驗(yàn)室鄧秀新院士團(tuán)隊(duì)揭示了新發(fā)掘的臍橙棕色突變體“宗橙”的突變機(jī)理，并進(jìn)一步解析了柑果類果實(shí)發(fā)育過程中葉綠素降解和類胡蘿卜素合成的協(xié)同調(diào)控機(jī)制，為未來柑橘色澤品質(zhì)改良提供了重要理論依據(jù)。相關(guān)研究成果發(fā)表在國際學(xué)術(shù)期刊Plant Physiology上。

 

　　柑橘是世界第一大水果，其栽培面積和產(chǎn)量均居果樹之首，具有非常重要的經(jīng)濟(jì)價值和營養(yǎng)價值。柑果是蕓香科柑橘屬植物特有的果實(shí)類型，具有區(qū)別于其它果實(shí)獨(dú)特的形態(tài)學(xué)特征。葉綠素降解和類胡蘿卜素積累是柑橘類果實(shí)成熟的必經(jīng)過程，對果實(shí)的色澤品質(zhì)和商品價值起決定性作用。柑橘果實(shí)中葉綠素和類胡蘿卜素含量的差異使其呈現(xiàn)出綠色、黃色、橙色、紅色甚至棕色等。近年來，學(xué)者們對柑橘葉綠素降解和類胡蘿卜素合成途徑已經(jīng)有了較多的研究，但關(guān)于這兩條代謝途徑協(xié)同調(diào)控的分子機(jī)制仍然知之甚少。

 

 

　　“宗橙”為三峽庫區(qū)秭歸縣“倫晚臍橙”果園里發(fā)現(xiàn)的一個芽變新品系，其果皮呈現(xiàn)獨(dú)特的棕色。研究對“宗橙”棕色果皮表型及其主要品質(zhì)性狀進(jìn)行了精細(xì)分析，采用多組學(xué)和多種遺傳資源整合策略鑒定到了突變基因——滯綠基因STAY-GREEN（SGR），并結(jié)合生化手段解析了該突變體果皮葉綠素降解受阻和類胡蘿卜素積累增加的突變機(jī)制。

 

　　研究表明，柑橘中SGR基因存在兩個等位基因（CsSGRa和CsSGRb），與CsSGRa相比，CsSGRb由于序列變異引起的選擇性剪接而發(fā)生提前終止，產(chǎn)生截短型蛋白。“宗橙”中CsSGRa編碼區(qū)堿基突變形成了終止密碼子，使得蛋白編碼提前終止（命名為CsSGRaSTOP），CsSGRb基因序列與野生型一致。進(jìn)一步實(shí)驗(yàn)發(fā)現(xiàn)，僅CsSGRa具有葉綠素降解活性，CsSGRaSTOP和CsSGRb均喪失了降解葉綠素的功能；CsSGRa和CsSGRb均可與類胡蘿卜素合成途徑限速酶CsPSY1互作，CsSGRaSTOP不能與CsPSY1互作，其可通過解除對CsPSY1的抑制作用促進(jìn)類胡蘿卜素的合成。

 

　　綜上，CsSGRa的突變導(dǎo)致了宗橙果皮葉綠素降解受阻和類胡蘿卜素含量顯著增加，綠色和橙色疊加使其最終呈現(xiàn)出棕色表型。該研究闡明了“宗橙”突變的分子機(jī)制，揭示了SGR在調(diào)控柑果類果實(shí)成熟過程中的重要作用，并首次發(fā)現(xiàn)柑橘中SGR等位基因的功能分化及其對葉綠素降解和類胡蘿卜素合成的獨(dú)特而精細(xì)的協(xié)同調(diào)控機(jī)制。

 

　　華中農(nóng)業(yè)大學(xué)園藝林學(xué)學(xué)院鄧秀新院士和美國紐約市立大學(xué)Eleanore T. Wurtzel教授為該論文的共同通訊作者，鄧秀新院士課題組朱凱杰博士為該論文的第一作者。西班牙瓦倫西亞農(nóng)業(yè)研究所、美國紐約植物園、秭歸縣柑桔良種繁育中心等單位也參與了此項(xiàng)研究。該研究在國家重點(diǎn)研發(fā)計劃和國家自然科學(xué)基金的資助下完成。

 

　　【英文摘要】

 

　　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 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 protein （SGR）， 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 make 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.

 

　　論文鏈接：

 

　　https://academic.oup.com/plphys/advance-article/doi/10.1093/plphys/kiab291/6308950