Michelia crassipes is a great ornamental plant, the flowers of which have high economic value. In this study, we employed headspace solid-phase microextraction (HS–SPME) combined with gas chromatography high-resolution mass spectrometry (GC–HRMS) for the first time to identify the volatile compounds emitted from different organs of M. crassipes flowers at different flowering stages. M. crassipes flower odor comprises 69 volatile compounds that are dominated by terpenes constituting 84% of collected volatiles. It was found that α-guaiene, β-caryophyllene and germacrene B had the highest relative amounts, while ethyl 3-methyl valerate, methyl benzoate and β-damascone had the highest odor activity values (OAVs). This contributed to the complex fruity, woody and floral aromas of M. crassipes. Total odor emission increased along the flower blooming, which was most abundant in the pistil followed by tepals and stamens. Paraffin sections of M. crassipes flower organs showed the highest density of oil secretory cells in the pistil at the full flowering stage, which was positively correlated with total odor release. The scent of the pistil and tepals was characterized by terpenes, whereas stamens was characterized by benzenoids. We suggest that the benzenoids in stamens might contribute to pollinator attraction in M. crassipes.

In lily reproduction, the mechanism of formation of bulbs has been a hot topic. However, studies on stem bulblet formation are limited. Stem bulblets, formed in the leaf axils of under- and above-ground stems, provide lilies with a strong capacity for self-propagation. First, we showed that above-ground stem bulblets can be induced by spraying 100 mg/L 6-BA on the LA hybrid lily ‘Aladdin’, with reduced endogenous IAA and GA₄ and a higher relative content of cytokinins. Then, expression patterns of three potential genes (two KNOTTED1-like homeobox (KNOX) and one partial BEL1-like homeobox (BELL)), during stem bulblet formation from our previous study, were determined by RT-qPCR, presenting a down-up trend in KNOXs and a rising tendency in BELL. The partial BELL gene was cloned by RACE from L. ‘Aladdin’ and denoted LaBEL1. Physical interactions of LaKNOX1-LaBEL1 and LaKNOX1-LaKNOX2 were confirmed by yeast two-hybrid and bimolecular fluorescence complementation assays. Furthermore, hormonal regulatory patterns of single LaKNOX1, LaKNOX2, LaBEL1, and their heterodimers, were revealed in transgenic Arabidopsis, suggesting that the massive mRNA accumulations of LaKNOX1, LaKNOX2 and LaBEL1 genes during stem bulblet formation could cause the dramatic relative increase of cytokinins and the decline of GAs and IAA. Taken together, a putative model was proposed that LaKNOX1 interacts with LaKNOX2 and LaBEL1 to regulate multiple phytohormones simultaneously for an appropriate hormonal homeostasis, which suggests their potential role in stem bulblet formation in L. ‘Aladdin’.

Lilies (Lilium spp.) are globally important ornamental crops which are constrained by their narrow thermal tolerance range. However, tiger lily (Lilium lancifolium), a wild lily species, exhibits remarkable cold tolerance. Based on our previous findings, we proposed that LlR3MYB, an R3-MYB transcription factor (TF), confers cold tolerance via transcriptional regulation of flavonoid metabolism in tiger lily. Here, we revealed that LlR3MYB represents a unique CPC-type R3-MYB TF exhibiting a bifunctional role in flavonoid metabolism. Specifically, LlR3MYB suppresses anthocyanin biosynthesis while promoting non-anthocyanin flavonoid accumulation (i.e. flavonols, flavones, and chalcones) responding to cold stress. Overexpression of LlR3MYB in tobacco and tiger lily increased total flavonoid content but reduced anthocyanin levels, consistent with the upregulation of early biosynthesis genes (e.g. CHS and FLS) and repression of late biosynthesis genes (e.g. DFR and ANS) in the pathway. In contrast, silencing LlR3MYB in tiger lily reduced total flavonoid production, enhanced anthocyanin accumulation, and compromised cold resistance. Mechanistically, LlR3MYB can directly bind to the AC-I element (ACCTACC) and MBSI motif (CAACGGTT) in the LlCHS2 promoter and activating its transcription, with enhanced activation under low temperature conditions. Mutations of critical residues within the C1/C2 repressor motifs may endow LlR3MYB with this transcriptional activation function. Furthermore, LlDREB can directly bind to the DRE motif (ACCGAC) in the LlR3MYB promoter and activating its transcription in a low-temperature-dependent manner. Our findings uncover a branch-specific regulatory mechanism by which MYB TFs fine-tune flavonoid biosynthesis, highlighting their essential role in plant cold stress responses.

Magnolia cavaleriei var. platypetala ‘Tanchun’ is a newly registered flower variety in China, known for its characteristic floral aroma that intensifies toward full bloom. However, the composition of the volatiles of this aromatic flower remains uncharacterized. Here, we compared the volatile organic compound composition of Tanchun through gas chromatography–mass spectrometry and comparative transcriptome sequencing analyses of the stamen (S), pistil (P), and petals (T) during flower development, i.e., the bud (S1), semi-opened (S2), and bloom (S3) stages. We present a first comprehensive profile of 1395 metabolites from Tanchun’s floral organs. Terpenoids (26.2%) constituted the largest chemical group, followed by esters (17.52%), nitrogen compounds (9.83%), hydrocarbons (8.11%), alcohols (7.97%), aldehydes (6.53%), and others. We found that volatile organic compound (VOC) accumulation was both spatiotemporal and stage-specific. The S1 and S2 transition was characterized by scent notes of green, herbal, and waxy aromas, while the S2 and S3 shift exhibited a richer profile of fruity, sweet, and creamy notes, primarily in petals. A comparative VOC and transcriptomic analysis revealed that petals activate pathways for structural expansion and precursor mobilization, stamens enhance lipid and terpenoid metabolism, and pistils maintain a conserved profile. Importantly, the S1 and S2 transition in petals establishes the biochemical foundation by activating acyl-CoA, phenylpropanoid, and terpenoid synthesis pathways, which enables the activation of the butanoate metabolism pathway at S3, leading to the production of ester-rich compounds that define the floral scent. The transition to full bloom involves a shift to energy-efficient volatile biosynthesis, supported by carbohydrate restructuring and phytohormonal regulation. Our results provide the first comprehensive volatilome and transcriptome resource for ‘Tanchun’, revealing a highly efficient, multi-stage strategy for floral fragrance biosynthesis. This work lays a molecular foundation for future horticultural improvement and biotechnological applications in the flavor and fragrance industries.