Abstract Detail

Evolutionary Developmental Biology (Evo-Devo)

Khojayori, Farah [1], Zhang, Jingbo [1], Kramer, Elena [2], Davis, Charles [3], Zhang, Wenheng [1].

CYC2-like genes elucidate floral symmetry evolution following a major biogeographic disjunction.

Recent studies indicate that CYCLOIDEA2- (CYC2-) like genes have likely played an important role in the evolution of floral symmetry in Malpighiaceae. Two copies of CYC2, CYC2A and CYC2B, arose from a gene duplication in the common ancestor of the family. These genes are differentially expressed among New World (NW) species exhibiting the typical floral zygomorphy: CYC2A is expressed in the dorsal banner petal and adjacent lateral petals; CYC2B is restricted to the dorsal banner petal. Loss of the obligate NW oil bee pollinators is associated with the loss of NW floral morphology in Old World (OW) Malpighiaceae. Among the seven OW clades, the acridocarpoids are comprised of the African and Malagasy Acridocarpus (ca. 32 species) and the Southeast Asian Brachylophon (ca. 2 species). Zygomorphic flowers of Acridocarpus consist of two prominent dorsal petals, two lateral petals, and one ventral petal. The flowers of Brachylophon, in contrast, are actinomorphic. We previously demonstrated for Acridocarpus natalitius and A. zanzibaricus that CYC2B has likely been lost, and that CYC2A expression was shifted to the dorsal and lateral petals coinciding with their altered morphology. Here, we report that Brachylophon curtisii contains both CYC2 genes, with BcCYC2A maintaining the ancestral NW expression, while BcCYC2B is only expressed in the stamens. We also demonstrate that the evolution of CYC2 genes in Acridocarpus is more complicated than previously thought. CYC2B homologs have been lost, independently, several times in the genus; CYC2A, in contrast, was largely maintained with the exception of certain species in which it was lost. Taken together, these results suggest that the ancestral NW expression of CYC2 genes was modified independently within Acridocarpus and Brachylophon, implying that the most recent common ancestor of these two genera possessed the NW floral zygomorphy. This model supports the conclusion that the ancestors of the acridocarpoids likely diverged quickly upon their arrival to the OW, and that their ancestral NW floral zygomorphy was subsequently modified independently, presumably in response to different pollinator selective regimens in Africa and Southeast Asia.

1 - Virginia Commonwealth University, Department of Biology, 1000 West Cary Street, Richmond, VA, 23284, USA
2 - Harvard University, 16 Divinity Avenue, Cambridge, MA, 02138, USA
3 - Harvard University, Department of Organismic and Evolutionary Biology / Harvard University Herbaria, 22 Divinity Ave, Cambridge, MA, 02138, USA

Keywords:
CYCLOIDEA2
Brachylophon
Acridocarpus
Malpighiaceae
reversal to floral actinomorphy
dispersal to the Old World
floral symmetry evolution.

Presentation Type: Oral Paper
Session: 34, Evo-Devo
Location: Sundance 2/Omni Hotel
Date: Wednesday, June 28th, 2017
Time: 10:15 AM
Number: 34009
Abstract ID:494
Candidate for Awards:Katherine Esau Award