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Plant development and evolution: Lessons learned from candidate genes

Hu, Jer-Ming [1], Lu, Chia-Ying [1].

Petaloidy and expression of petal identity genes in Mussaenda pubescens (Rubiaceae).

Recent studies suggested that all of the angiosperms may share a similar developmental program for floral organ formation. We are interested in floral organ transformation for plants forming petaloid structures that replaces the function originally possessed by true petals. Petaloid structures are found in many flowering plants, and can be classified as extrafloral petaloids, such as the showy bracts in flowering dogwoods; and floral petaloids, such as the enlarged showy calyx-lobes (calycophylls) in Mussaenda (Rubiaceae). Calycophylls of the species Mussaenda pubescens are found in the outmost flowers of inflorescences, and usually form one calycophyll per flower. Calycophylls are mostly leaf-shaped, but have several petal-like morphologies, such as bright color, papillate epidermis, and loose mesophylls, features that are generally thought to attract pollinator. Based on recent molecular studies on floral genes in Arabidopsis thaliana, petaloidy could be simply explained by an ectopic expression of genes that control petal development, because overexpressing petal identity genes can convert leaves to petaloid structures in A. thaliana. Therefore, the formation of calycophylls in Mussaenda could be regulated by petal identity genes. We have cloned five floral organ identity gene homologues from M. pubescens: one A class homologue (MupAP1), one E class homologue (MupSEP), and three B class gene homologues (MupGLO, MupDEF, and MupTM6). RT-PCR results showed that except for MupGLO, all the other identified genes are expressed in all floral parts, including small and enlarged sepals, petals/stamens, carpels, and fruits. In contrast, MupGLO is expressed in petals/stamens, carpels, and fruits, and in some populations, it is found expressed in small, but not enlarged sepals. The result is incongruent with our hypothesis, therefore, suggests that the formation of petaloid sepals in M. pubescens may be regulated by other unidentified factors that current floral gene regulation model could not explain.

1 - National Taiwan University, Institute of Ecology and Evolutionary Biology, Rm1227, Life Science Building, 1 Roosevelt Road, Sect.4, Taipei, 106, Taiwan

Mussaenda pubescens
gene expression .

Presentation Type: Symposium
Session: 54-4
Location: Ballroom 1 (Cliff Lodge)
Date: Wednesday, August 4th, 2004
Time: 2:45 PM
Abstract ID:225

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