Development of a Purple-Leaf Perillene Chemotype Line in Perilla frutescens Reveals Incomplete Linkage with Leaf Color

Perilla frutescens(L.) Britt. (P. frutescens) is an important medicinal and aromatic plant, whose leaf color and chemotype strongly influence its medicinal quality and economic value. All the previously discovered perillene (PL)-typeP. frutescensare double-sided green, and whether the PL-type trait is tightly linked with the green-leaf trait in genetics remains to be clarified. This study aimed to address this question and attempt to create purple-leaf PL-type germplasm through perillaldehyde (PA) × PL hybridization. Three parallel experiments were conducted using purple-leaf PA-typeP. frutescensas male parents and green-leaf PL-typeP. frutescensas female parents. Chemotypes were identified by gas chromatography (GC). Association analyses between leaf color and chemotype were performed in segregating F2populations. Genes involved in leaf color formation and PL biosynthesis were mapped onto the published Hoko-3 reference genome to provide genomic evidence for the genetic relationship between the two traits. All F1individuals were uniformly PA-type. The three F2populations exhibited distinct leaf color–chemotype association patterns: Z01 (n= 118) showed a strong association (Fisher’s exactp= 9.13 × 10−10; φ = 0.564), Z02 (n= 117) showed no detectable association (p= 0.9; φ = 0.012), and Z03 (n= 88) showed a moderate association (p= 0.00669; φ = 0.289). Importantly, purple-leaf PL-type recombinants were obtained in F2populations and stably maintained through subsequent generations (F3–F5), demonstrating that the PL-type trait is not tightly linked with the green-leaf trait inP. frutescens.Genomic mapping genes related to leaf color and PL biosynthesis are distributed across multiple chromosomes and usually present as multiple loci, which is consistent with the pattern of incomplete linkage. The PL-type trait is recessive and not genetically tightly linked to the green-leaf traits inP. frutescens. The successful creation of a purple-leaf PL-type germplasm breaks the historical phenotypic constraint and provides a novel material for further dissection of the molecular mechanisms regulating secondary metabolism and organ coloration inP. frutescens.