To understand the molecular mechanism underlying tepal development and pigmentation in Lilium tsingtauense Gilg, we performed whole-transcriptome profiles from closed buds at the greenish tepal stage (CBS), the full-bloom with un-horizontal tepal stage (UFS), and the completely opened bud with reflected tepal stage (RFS) of L. tsingtauense. More than 95 699 transcripts were generated using a de novo assembly approach. Gene ontology and pathway analysis of the assembled transcripts revealed carbon metabolism is involved in tepal development and pigmentation. In total, 8171 differentially expression genes (DEGs) in three tepal stages were identified. Among these DEGs, ~994 genes putatively encoded transcription factors (TFs), whereas 693 putatively encoded protein kinases. Regarding hormone pathways, 51 DEGs involved in auxin biosynthesis and signalling and 10 DEGs involved in ethylene biosynthesis and signalling. We also isolated seven LtEXPANSINs, including four EXPAs, one EXPB, one EXLA and one EXLB. LtEXLB1 (GenBank: MN856627) was expressed at higher levels in UFS and RFS, compared with CBS. Silencing LtEXLB1 in leaf discs and tepals by virus-induced gene silencing significantly decreased cell expansion under rehydration conditions. Further analysis revealed that more cell numbers were existed in the abaxial and adaxial subepidermis in the silenced LtEXLB1 samples. As the first transcriptome of L. tsingtauense, the unigenes are a valuable resource for future studies on tepal development, and LtEXLB1 functions in cell expansion.

Flower bud differentiation is of great significance for understanding plant evolution and ecological adaptability. The development of flower buds and mixed buds in the dichasial inflorescence of Geranium koreanum was described in this paper. The morphogenesis, surface structure, and organ morphology at different growth stages of G. koreanum buds were examined in detail using scanning electron microscope and stereo microscope. The development of mixed buds started from the flattened apical meristem. The stipule and leaf primordia arose first. Subsequently, the hemispherical meristem was divided into two hemispheres, forming a terminal bud and floral bud primordia, followed by lateral bud differentiation. The formation of the terminal and lateral buds of G. koreanum was sequential and their differentiation positions were also different. The floral bud primordia would develop into two flower units and four bracts. The primordia of a flower bud first formed the sepal primordia, then the stamen and petal primordia, and finally the pistil primordia. Compared to the stamen primordia, the growth of the petal primordia was slower. Finally, all organs, especially the petals and pistil, grew rapidly. When the pistil and petals exceeded the stamens and the petals changed color, the flower bud was ready to bloom.