Genomic and Transcriptomic Analyses Illuminates Unique Traits of Elusive Night Flowering Jasmine Parijat (Nyctanthes arbor-tristis)

The night-flowering Jasmine, Nyctanthes arbor-tristis also known as Parijat, is a perennial woody shrub belonging to the family Oleaceae. It is popular for its fragrant flowers that bloom in the night and is a potent source of secondary metabolites. However, knowledge about its genome and the expression of genes regulating flowering or secondary metabolite accumulation is lacking. In this study, we generate whole genome sequencing data to assemble the first de novo assembly of Parijat and use it for comparative genomics and demographic history reconstruction. The temporal dynamics of effective population size (Ne) experienced a positive influence of colder climates suggesting the switch to night flowering may have provided an evolutionary advantage. We employed multi-tissue transcriptome sequencing of floral stages/parts to obtain insights into the transcriptional regulation of nocturnal flower development and the production of volatiles/metabolites. Tissue-specific transcripts for mature flowers revealed key players in circadian regulation and flower development, including auxin pathway and cell wall modifying genes. Furthermore, we identified tissue-specific transcripts responsible for producing numerous secondary metabolites, mainly terpenoids and carotenoids. The diversity and specificity of Terpene Synthase (TPS) and CCDs (Carotenoid Cleavage Deoxygenases) mediate the bio-synthesis of specialised metabolites in Parijat. Our study establishes Parijat as a novel non-model species to understand the molecular mechanisms of nocturnal blooming and secondary metabolite production.

夜花茉莉（Nyctanthes arbor-tristis），亦称帕里贾特，为茜草科多年生木本灌木。其夜间绽放的芬芳花朵备受赞誉，且为次生代谢物的丰富来源。然而，关于其基因组及其调控开花或次生代谢物积累的基因表达的知识尚显匮乏。在本研究中，我们生成了全基因组测序数据，组装了帕里贾特的首次从头组装，并将其用于比较基因组学和种群历史重建。有效种群大小（Ne）的时间动态受到寒冷气候的积极影响，暗示夜间开花的转变可能为进化提供了优势。我们采用了花阶段/部位的多个组织转录组测序，以获取对夜间花朵发育转录调控及挥发性/代谢物生产的洞察。成熟花朵的特异性转录物揭示了昼夜节律调控和花朵发育中的关键角色，包括生长素途径和细胞壁修饰基因。此外，我们还鉴定了负责产生多种次生代谢物（主要为萜类和类胡萝卜素）的特异性转录物。萜类合成酶（TPS）和胡萝卜素裂解脱氧酶（CCDs）的多样性和特异性在帕里贾特中调节了特异代谢物的生物合成。本研究将帕里贾特确立为一个新的非模式物种，以理解夜间开花和次生代谢物生产的分子机制。