Comparative and Spatial Transcriptome Analysis of Rhododendron decorum Franch. During the Flowering Period and Revelation of the Plant Defense Mechanism.

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Rhododendron is a globally distributed and extensive genus, comprising over 1000 species. In the southwestern mountains of China, there exists a remarkable diversity of Rhododendron, with Yunnan Province alone harboring more than 600 species. R. decorum Franch. has long been utilized by local communities for its medicinal and edible properties. However, the transcriptional regulation function, medicinal properties, and edibility characteristics of R. decorum Franch. currently lack a solid theoretical basis. Total RNA was extracted from leaves, corollas and androecium/gynoecium of R. decorum Franch. in Heqing county, followed by the construction of cDNA libraries and the de novo assembly of transcriptomes. A total of 63,050 unigenes were extracted from the flowers and leaf organs of R. decorum Franch. Among these unigenes, 43,517 were predicted to be coding sequences, with 32,690 being effectively annotated. Differential gene expression enrichment was observed among different organs within their respective transcriptomes; notably floral organs exhibited significant defense against plant diseases along with signal transduction functions. Furthermore, during the flower harvesting period, all floral organs exhibited gene enrichment pathways associated with carbohydrate metabolism. Additionally, the stamen and pistil displayed flavonoid metabolism pathways, suggesting their potential applications as functional food or medicine. Our results shed light on plant-pathogen defense mechanisms and the molecular bias of flavonoids biosynthesis on flower organs during the flowering period, which might help to understand the consumption of R. decorum Franch. corollas by the Bai nationality of Heqing county.