Sequence and Expression Studies of A‐, B‐, and E‐Class MADS‐Box Homologues inEupomatia(Eupomatiaceae): Support for the Bracteate Origin of the Calyptra

Abstract

Eupomatia (Magnoliales, Eupomatiaceae) has flowers that bear a calyptra, an unusual organ that encloses the floral bud. The structural homology and evolutionary derivation of the calyptra are unknown, although some have proposed that it is a bract, while others favor a derivation from the perianth. To address the evolutionary origin of the calyptra, we isolated, sequenced, and characterized the expression of A‐, B‐, and E‐class MADS‐box homologues from Eupomatia bennettii and a close relative, Magnolia grandiflora (Magnoliaceae). The expression patterns of organ identity genes in floral organs of Eupomatia and Magnolia were very similar. However, the expression patterns of these MADS‐box genes indicated that the ABC model is not strictly applicable to either Eupomatia or Magnolia. For example, A‐class homologues were expressed in carpels and leaves of both Eupomatia and Magnolia. In the calyptra, expression levels of B‐ and E‐class homologues were low and almost identical to those observed in leaf tissue....