Cloning of the Brcer1 gene involved in cuticular wax production in a glossy mutant of non-heading Chinese cabbage (Brassica rapa L. var. communis)

Abstract

Cuticular wax is a complex mixture of very-long-chain fatty acid derivatives. The wax on the surface of plants serves as a protective barrier to reduce non-stomatal water loss and environmental damage. However, the loss of wax may lead to a glossy phenotype, which is an favorable trait in leafy vegetables. The mechanism of glossy mutants in non-heading Chinese cabbage (Brassica rapa L. var. communis) has not been studied yet. In this study, scanning electron microscopy (SEM) showed that the cuticular wax on the leaves and stem of a glossy mutant was dramatically reduced compared with that of the wild-type plant. Transmission electron microscopy (TEM) revealed that the cuticle ultrastructure of glossy mutant leaf and stem were altered when compared with the wild type. A cuticle wax analysis showed the total wax content of leaves, as well as alkanes, ketones and alcohols, was decreased. A genetic analysis indicated that the glossy phenotype was controlled by a single gene. Based on a homology analysis, the Brcer1 gene was identified as the candidate gene controlling the glossy phenotype. In the glossy mutant, a 39-bp deletion leads to an mRNA disruption and reduces the expression of the BrCER1 gene. Sequence analysis showed that a loss of function mutation in the Brcer1 gene was different from that of Cgl1, which was previously shown to be responsible for the glossy phenotype in B. oleracea, showing typical parallel selection. These findings provide a better understanding of the cuticular wax biosynthesis pathway and offer important information for molecular-assisted breeding of non-heading Chinese cabbage (B. rapa L. var. communis).