The Brassica rapa elongated internode (EIN) gene encodes phytochrome B.

The elongated internode (ein) mutation of Brassica rapa leads to a deficiency in immunochemically detectable phytochrome B. Molecular analysis of the PHYB gene from ein indicates a deletion in the flanking DNA 5' of the ATG start codon, which could interfere either with PHYB transcription or processing of the PHYB transcript. Restriction fragment length polymorphisms and inverse PCR fragments generated from the PHYB gene of wild-type and ein seedlings demonstrate the deletion to be 500 bp in length. Seedlings of heterozygote, EIN/ein, contain about 50% of the level of immunochemically detectable phytochrome B of equivalent wild-type EIN/EIN seedlings. Etiolated seedlings of EIN/ein show a responsiveness to red light almost intermediate between that of ein/ein and EIN/EIN homozygotes. Furthermore, whereas the ein/ein homozygote is poorly responsive to low red/far-red ratio light, the presence of one functional allele of EIN in the heterozygote confers an elongation response intermediate between that of the homozygotes EIN/EIN and ein/ein in these light conditions. The partial dominance of ein indicates a close relationship between phytochrome B level and phenotype.