An LTR retrotransposon insertion was the cause of world’s first low erucic acid Brassica rapa oilseed cultivar

Abstract

Brassica rapa is an important oilseed crop species next to B. napus in Brassicaceae. However, genetic improvement of B. rapa oilseeds has not been intensively conducted compared to B. napus, which resulted in the limited number of low erucic acid (LEA) cultivars, which is an essential trait for edible oil materials. Candle and Tobin are LEA B. rapa cultivars bred in Canada that are closely related to each other; however, the causal mutation has not been identified. This study was initially aimed to investigate whether the alleles of BrFAE1, the gene encoding a key enzyme for erucic acid synthesis, in Candle and Tobin have mutations impairing their functions. An insertion of the long terminal repeat (LTR) retrotransposon, designated as BRACOPIA, was identified in the 5′ end of the coding region of the gene in both Candle and Tobin. BRACOPIA disrupted the transcription in developing seeds, resulting in a loss of function allele designated as brfae1re. Next, we found that Span, the world’s first LEA B. rapa cultivar developed in Canada, has brfae1re, suggesting that the BRACOPIA insertion is the founder mutation of Canadian LEA B. rapa cultivars. Finally, we investigated the distribution of BRACOPIA family retrotransposons in the Brassica genus, and found that they are present in both the A and C genomes, but the activity has been kept rather modest. Since brfae1re is easily distinguishable from the wild-type allele by PCR, the identification of this mutation could enhance LEA breeding in B. rapa.