Bixin is a commercially valuable apocarotenoid pigment found in the seed aril of Bixa orellana. The dynamics and regulation of its biosynthesis and accumulation during seed development remain largely unknown. Here, we combined chemical, anatomical, and transcriptomic data to provide stage-specific resolution of the cellular and molecular events occurring during B. orellana seed development. Seeds at five developmental stages (S1–S5) were used for analysis of bixin content and seed anatomy, and three of them (S1, S3, and S4) were selected for Illumina HiSeq sequencing. Bixin accumulated in large quantities in seeds compared with other tissues analyzed, particularly during the S2 stage, peaking at the S4 stage, and then decreasing slightly in the S5 stage. Anatomical analysis revealed that bixin accumulated in the large central vacuole of specialized cells, which were scattered throughout the developing mesotesta at the S2 stage, but enlarged progressively at later stages, until they occupied most of the parenchyma in the aril. A total of 13 million reads were generated and assembled into 73,381 protein-encoding contigs, from which 312 were identified as containing 1-deoxy-D-xylulose-5-phosphate/2-C-methyl-D-erythritol-4-phosphate (DOXP/MEP), carotenoid, and bixin pathways genes. Differential transcriptome expression analysis of these genes revealed that 50 of them were sequentially and differentially expressed through the seed developmental stages analyzed, including seven carotenoid cleavage dioxygenases, eight aldehyde dehydrogenases, and 22 methyltransferases. Taken together, these results show that bixin synthesis and accumulation in seeds of B. orellana are a developmentally regulated process involving the coordinated expression of DOXP/MEP, carotenoid, and bixin biosynthesis genes.

Bixin 是一种具有商业价值的类胡萝卜素色素，存在于Bixa orellana的种子假种皮中。在种子发育过程中其生物合成和积累的动态和调控在很大程度上仍然未知。在这里，我们结合了化学、解剖学和转录组学数据，以提供B. orellana期间发生的细胞和分子事件的阶段特异性分辨率种子发育。五个发育阶段 (S1–S5) 的种子用于分析 bixin 含量和种子解剖结构，并选择其中三个（S1、S3 和 S4）进行 Illumina HiSeq 测序。与分析的其他组织相比，Bixin 在种子中大量积累，特别是在 S2 阶段，在 S4 阶段达到峰值，然后在 S5 阶段略有下降。解剖学分析表明，bixin 聚集在特化细胞的大中央液泡中，这些液泡在 S2 阶段散布在整个发育中的种皮中，但在后期逐渐扩大，直到它们占据假种皮的大部分薄壁组织。总共生成了 1300 万个读数并组装成 73,381 个蛋白质编码重叠群，其中 312 个被鉴定为含有 1-deoxy-D-xylulose-5-phosphate/2-C-methyl-D-erythritol-4-phosphate (DOXP/MEP)、类胡萝卜素和 bixin 通路基因。对这些基因的差异转录组表达分析显示，其中 50 个在分析的种子发育阶段顺序差异表达，包括 7 个类胡萝卜素裂解双加氧酶、8 个醛脱氢酶和 22 个甲基转移酶。综上所述，这些结果表明，红木素在种子中的合成和积累 八种醛脱氢酶和 22 种甲基转移酶。综上所述，这些结果表明，红木素在种子中的合成和积累 八种醛脱氢酶和 22 种甲基转移酶。综上所述，这些结果表明，红木素在种子中的合成和积累B. orellana是一个发育调控过程，涉及 DOXP/MEP、类胡萝卜素和红木素生物合成基因的协调表达。