Daucus carota is a biennale crop that develops an edible storage root. Orange carrots, the most consumed cultivar worldwide, accumulate high levels of β-carotene and α-carotene in the storage root during secondary growth. Genes involved in β-carotene synthesis have been identified in carrots and unlike most species, D. carota has two ζ-carotene desaturase genes, named ZDS1 and ZDS2, that share 91.3 % identity in their coding regions. ZDS1 expression falls during leaf, but not root development, while ZDS2 is induced in leaves and storage roots of a mature plant. In this work, by means of post-transcriptional gene silencing, we determined that ZDS1 is essential for initial carrot development. The suppression of the expression of this gene by RNAi triggered a reduction in the transcript levels of ZDS2 and PSY2 genes, with a concomitant decrease in the carotenoid content in both, leaves and storage roots. On the contrary, transgenic lines with reduced ZDS2 transcript abundance maintain the same levels of expression of endogenous ZDS1 and PSY2 and carotenoid profile as wild-type plants. The simultaneous silencing of ZDS1 and ZDS2 resulted in lines with a negligible leaf and root development, as well as significantly lower endogenous PSY2 expression. Further functional analyses, such as a plastidial subcellular localization of ZDS1:GFP and the increment in carotenoid content in transgenic tobacco plants overexpressing the carrot ZDS1, confirmed that ZDS1 codifies for a functional enzyme. Overall, these results lead us to propose that the main ζ-carotene desaturase activity in carrot is encoded by the ZDS1 gene and ZDS2 gene has a complementary and non essential role.

中文翻译：

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胡萝卜（Daucus carota）中两个 ζ-胡萝卜素去饱和酶旁系同源物的不同作用：ZDS1 是植物发育和类胡萝卜素合成必不可少的功能基因

Daucus carota 是一种双年展作物，可培育出可食用的储藏根。橙色胡萝卜是世界上消费量最大的品种，在二次生长过程中，它在储藏根中积累了大量的 β-胡萝卜素和 α-胡萝卜素。已在胡萝卜中鉴定出参与 β-胡萝卜素合成的基因，与大多数物种不同，D. carota 有两个 ζ-胡萝卜素去饱和酶基因，命名为 ZDS1 和 ZDS2，它们的编码区具有 91.3% 的同一性。ZDS1 的表达在叶子而非根发育期间下降，而 ZDS2 在成熟植物的叶子和贮藏根中被诱导。在这项工作中，通过转录后基因沉默，我们确定 ZDS1 对胡萝卜的初始发育至关重要。RNAi 对该基因表达的抑制引发了 ZDS2 和 PSY2 基因转录水平的降低，伴随着叶和贮藏根中类胡萝卜素含量的降低。相反，ZDS2 转录本丰度降低的转基因株系保持与野生型植物相同的内源性 ZDS1 和 PSY2 表达水平以及类胡萝卜素谱。ZDS1 和 ZDS2 的同时沉默导致株系的叶和根发育可以忽略不计，并且内源性 PSY2 表达显着降低。进一步的功能分析，例如 ZDS1:GFP 的质体亚细胞定位和过表达胡萝​​卜 ZDS1 的转基因烟草植物中类胡萝卜素含量的增加，证实 ZDS1 编码了一种功能酶。全面的，