Sequence and expression studies of A-, B-, and E-class mads-box homologues in Eupomatia (Eupomatiaceae): support for the bracteate origin of the calyptra

• Published in: International journal of plant sciences Vol. 166; no. 2; pp. 185 - 198
• Main Authors: Kim, S, Koh, J, Ma, H, Hu, Y, Endress, P.K, Hauser, B.A, Buzgo, M, Soltis, P.S, Soltis, D.E
• Format: Journal Article
• Language: English
• Published: Chicago The University of Chicago Press 01-03-2005; University of Chicago, acting through its Press
• Subjects: Deoxyribonucleic acid; DNA; Evolutionary biology; Flowers & plants; Gene expression; Ribonucleic acid; RNA; real-time PCR; Eupomatia; alternative splicing; Magnolia; relative-quantitative-reverse transcriptase PCR; ABC model
• ISSN: 1058-5893; 1537-5315
• DOI: 10.1086/427479

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. In contrast, high levels of expression for B- and E-class homologues were observed in the stamens, staminodes, and carpels. These gene expression data agree with recent developmental data and the interpretation of the calyptra as a bract. We also report the presence of various forms of alternatively spliced mRNAs in the cDNA pool from floral organs, and the implications of these mRNAs are discussed.