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Summary: Habenaria radiata(Orchidaceae) has two whorls of perianth, comprising three greenish sepals, two white petals and one lip (labellum). By contrast, the pseudopeloric (with a decreased degree of zygomorphy) mutant cultivar of H. radiata, 'Hishou', has changes in the identities of the dorsal sepal to a petaloid organ and the two ventral sepals to lip‐like organs. Here, we isolated four DEFICIENS‐like and two AGL6‐like genes from H. radiata, and characterized their expression. Most of these genes revealed similar expression patterns in the wild type and in the 'Hishou' cultivar, except HrDEF‐C3.The HrDEF‐C3gene was expressed in petals and lip in the wild type but was ectopically expressed in sepal, petals, lip, leaf, root and bulb in 'Hishou'. Sequence analysis of the HrDEF‐C3loci revealed that the 'Hishou' genome harbored two types of HrDEF‐C3genes: one identical to wild‐type HrDEF‐C3and the other carrying a retrotransposon insertion in its promoter. Genetic linkage analysis of the progeny derived from an intraspecific cross between 'Hishou' and the wild type demonstrated that the mutant pseudopeloric trait was dominantly inherited and was linked to the HrDEF‐C3gene carrying the retrotransposon. These results indicate that the pseudopeloric phenotype is caused by retrotransposon insertion in the HrDEF‐C3promoter, resulting in the ectopic expression of HrDEF‐C3. As the expression of HrAGL6‐C2was limited to lateral sepals and lip, the overlapping expression of HrDEF‐C3and HrAGL6‐C2is likely to be responsible for the sepal to lip‐like identity in the lateral sepals of the 'Hishou' cultivar. Significance Statement: Unlike wild‐type Habenaria radiata flowers, which have a single modified medial petal formed into a lip, the mutant cultivar 'Hishou' flowers exhibit two additional lip‐like organs replacing the lateral sepals. Here, we identified the Hret2 retrotransposon insertion in the HrDEF‐C3 gene promoter as the cause of the pseudopeloric phenotype of 'Hishou'. Based on DEF‐ and AGL6‐like gene expression patterns in the wild type and 'Hishou', the differential dorsoventral expression of the HrAGL6‐C2 gene is correlated with the transformation of lateral sepals into lip‐like structures. [ABSTRACT FROM AUTHOR] |
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