Abstract Detail

Evolutionary Developmental Biology (Evo-Devo)

Khojayori, Farahnoz [1], Zhang, Jingbo [2], Kramer, Elena [3], Davis, Charles [4], Zhang, Wenheng [5].

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, termed CYC2A and CYC2B, are differentially expressed among New World (NW) species that exhibit the typical NW floral zygomorphy with a single, upright banner petal. CYC2A is expressed in the dorsal banner petal and adjacent lateral petals; CYC2B expression is restricted to the banner petal. Loss of the obligate NW oil-bee pollinators corresponds with loss of the NW floral morphology, principally among Old World (OW) Malpighiaceae. One of these OW clades, the acridocarpoids, is comprised of African and Malagasy Acridocarpus (ca. 32 species) and Southeast Asian Brachylophon (ca. 2 species). Flowers of Acridocarpus display a distinct pattern of floral zygomorphy with two dorsal petals, which are smaller than either of the two lateral petals or the single ventral petal. The flowers of Brachylophon, in contrast, are actinomorphic. Here, we have examined CYC2 evolution and expression in both zygomorphic and actinomorphic acridocarpoids to elucidate how the evolution of a conserved developmental program can clarify floral symmetry evolution following a major biogeographic shift. Previously, we isolated and tested the expression of CYC2A in Acridocarpus natalitius A. Juss and Acridocarpus zanzibaricus A. Juss.; CYC2B was hypothesized to be lost. We have since isolated both CYC2A and CYC2B from seven phylogenetically diverse species of Acridocarpus and Brachylophon curtisii Oliv. Among these species, we found that CYC2A is broadly expressed in the two dorsal and two lateral petals of A. natalitius and A. zanzibaricus. We now demonstrate that the expression of AzCYC2B in A. zanzibaricus is restricted to the two dorsal petals corresponding to its zygomorphic corolla. In B. curtisii, BcCYC2A is expressed in four petals; BcCYC2B expression is lost entirely in the corolla. These results suggest that after Acridocarpus and Brachylophon split, Brachylophon further lost CYC2 function such that BcCYC2B is absent and that BcCYC2A varies in a manner that is not consistent with the morphology. Taken together, these results elucidate the evolution of floral symmetry through modification of a conserved genetic program following a major biogeographic disjunction, presumably as a response to different pollinator selective regimens in Africa and Southeast Asia.

1 - Virginia Commonwealth University, Biology, 1000 West Cary Street, Richmond, VA, 23284, United States
2 - Department Of Biology, Virginia Commonwealth University, 1000 West Cary Street, Life Science Building 336, Richmond, VA, 23284, United States
3 - Harvard University, Organismic and Evolutionary Biology, 16 Divinity Avenue, Biological Laboratories 1119, Cambridge, MA, 02138, USA
4 - Harvard University Herbaria, Organismic and Evolutionary Biology, 22 Divinity Avenue, Cambridge, Massachusetts, 02138, United States
5 - Virginia Commonwealth University, Department Of Biology, 1000 W Cary Street, Richmond, VA, 23284, United States

Keywords:
CYCLOIDEA2
Floral zygomorphy
Floral actinomorphy
reversal
Malpighiaceae
Brachylophon
Acridocarpus
floral symmetry evolution
biogeographic disjunction.

Presentation Type: Oral Paper
Session: 20, Evolutionary Developmental Biology (Evo-Devo) I
Location: 113/Mayo Civic Center
Date: Tuesday, July 24th, 2018
Time: 9:15 AM
Number: 20006
Abstract ID:926
Candidate for Awards:Katherine Esau Award