Analysis of the emitted pattern of floral volatiles and cloning and functional analysis of the PsuLIS gene in tree peony cultivar ‘High Noon’

The floral volatiles, many of which have fragrances, are one of the important quality characteristics of ornamental plants. Tree peony (Paeonia suffruticosa) is a famous traditional Chinese flower that is well-known in many countries around the world. However, the composition and formation mechanism of volatiles in tree peony flowers is unclear. Here, we analyzed the pattern of floral volatiles emitted and further cloned and analyzed the function of the PsuLIS (linalool synthetase) gene in cultivated tree peony cultivar ‘High Noon’ cultivated in the field. 49 compounds of floral volatiles were detected by using GC–MS in cultivated tree peony cultivar ‘High Noon’, with linalool having the highest content among all substances, which is much higher than that of other substances. Their relative content was separately highest at full blooming during the flowering process and at petals in various floral organ. The diurnal change of floral volatiles is highest during 10:00–12:00 and lowest during 16:00–18:00. Furthermore, the PsuLIS gene was cloned with an open reading frame of 1698 bp and encodes 565 amino acids. The phylogenetic analysis showed that the protein of PsuLIS has the closest evolutionary relationship with LIS in Actinidia arguta. The expression pattern of the PsuLIS gene, which exhibits its highest expression during the full blooming stage, in petals and from 10:00–12:00, demonstrated consistency with the emission pattern of linalool and displayed a significant positive correlation. Additionally, tree peony cultivar ‘High Noon’ plants were obtained through knockdown using the virus-induced gene silencing (VIGS) system. The relative expression of the PsuLIS gene in transient overexpression plants and knockdown plants were separately increasing by 3.8 times and decreasing by 74.7% compared to wild type plants, and the expression pattern of the PsuLIS gene was consistent with the variation trend observed in linalool content across different genotype cultivated tree peony cultivar ‘High Noon’ plants. The recombinant PsuLIS protein can convert geranyl diphosphate (GPP) to linalool in vitro. The aforementioned findings indicate that the PsuLIS gene plays a crucial role in regulating linalool synthesis in cultivated tree peony cultivar ‘High Noon’, and laying the foundation for cultivating different fragrance types of peonies.