The Identification of A-, B-, C-, and E-Class MADS-box Genes and Implications for Perianth Evolution in the Basal Eudicot Trochodendron aralioides (Trochodendraceae)

Trochodendron aralioides is the sole member of the family Trochodendraceae, which belongs to the basal eudicots, has vesselless wood, and lacks a distinct perianth. Our observations confirmed that there are numerous perianth-like structures and that the number of these structures differs between protandrous and protogynous flowers and among the positions within an inflorescence. The epidermal cells on many floral parts of T. aralioides are papillate or conical, similar to the ones of ordinary showy petals of other species. The data in this article support the hypothesis that the perianth of Trochodendron has been secondarily lost and suggest that some aspects of petal identity, e.g., papillate cells, have been retained that might be important for pollinator attraction. We have identified 11 homologues of floral organ identity genes - two A-class, three B-class, two C-class, and four E-class homologous genes - from T. aralioides. Phylogenetic analysis shows that all of the genes arose before a major duplication of MADS-box genes at the base of the core eudicots. Expression patterns for those floral organ identity gene homologues was determined by reverse transcriptase PCR, which showed variations that do not conform well to the current floral ABCDE model. In addition, all paralogous genes have distinct expression patterns, suggesting that they had undergone functional divergence. © 2007 by The University of Chicago. All rights reserved.