Pod lignin biosynthesis contributes to pre-harvest sprouting tolerance of rapeseed

Pre-harvest sprouting (PHS) poses a major hazard to rapeseed ( Brassica napus L.) production, particularly under rainy, moist conditions during harvest season. PHS tolerance mainly depends on seed dormancy and pericarp structure in other crops. However, little was known about the mechanisms underlying PHS tolerance in rapeseed. In this study, an elite PHS-tolerant genotype was screened from 750 global rapeseed germplasm resources by pod imbibition and seed germination assays. Results of imbibition dynamics have shown that the water absorption was slower in pod shell and seeds within pod of the PHS-tolerant genotype. The tolerant genotype also had higher pod shell thickness, cellulose content, and lignin content. The pod shell of the tolerant genotype was significantly enriched in a large number of differential metabolites involved in the phenylpropanoid metabolism pathway, which contribute to lignin biosynthesis. Moreover, lignin synthesis related genes BnaPAL4 , Bna4CL1 , BnaCCR1 , BnaHST and BnaPER42 significantly more expressed in the PHS-tolerant genotype than in the PHS-sensitive genotype. More lignin accumulation in the pod could protect rapeseed from PHS by decreasing the pericarp permeability. All these findings could provide valuable genetic resources for the breeding of PHS-tolerant rapeseed cultivars and understanding of PHS mechanism in Brassica species. • A PHS tolerant elite genotype, which has lost seed dormancy, was screened from 750 global rapeseed germplasm resources. • Pod shell might impart barriers to the seeds by restricting water availability essential for PHS tolerance in rapeseed. • Pod shell thickness is inversely correlated with seed germination in pod and occurrence of PHS. • More lignin accumulation in pod could protect rapeseed from PHS by decreasing pericarp permeability.