Homologs of LEAFY and UNUSUAL FLORAL ORGANS Promote the Transition From Inflorescence to Floral Meristem Identity in the Cymose Aquilegia coerulea

Bharti Sharma; Clara Meaders; Damien Wolfe; Lynn Holappa; Cristina Walcher-Chevillet; Elena M Kramer

doi:10.3389/fpls.2019.01218

Homologs of LEAFY and UNUSUAL FLORAL ORGANS Promote the Transition From Inflorescence to Floral Meristem Identity in the Cymose Aquilegia coerulea

Front Plant Sci. 2019 Oct 4:10:1218. doi: 10.3389/fpls.2019.01218. eCollection 2019.

Authors

Bharti Sharma^{1

2}, Clara Meaders^{2

3}, Damien Wolfe¹, Lynn Holappa², Cristina Walcher-Chevillet², Elena M Kramer²

Affiliations

¹ Department of Biological Sciences, California State Polytechnic University, Pomona, CA, United States.
² Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, United States.
³ Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, United States.

Abstract

Homologs of the transcription factor LEAFY (LFY) and the F-box family member UNUSUAL FLORAL ORGANS (UFO) have been found to promote floral meristem identity across diverse dicot model systems. The lower eudicot model Aquilegia produces cymose inflorescences that are independently evolved from the well-studied cymose models Petunia and tomato. We have previously characterized the expression pattern of the Aquilegia homolog AqLFY but in the current study, we add expression data on the two UFO homologs, AqUFO1 and 2, and conduct virus-induced gene silencing of all the loci. Down-regulation of AqLFY or AqUFO1 and 2 does not eliminate floral meristem identity but, instead, causes the transition from inflorescence to floral identity to become gradual rather than discrete. Inflorescences in down-regulated plants generate several nodes of bract/sepal chimeras and, once floral development does commence, flowers initiate several whorls of sepals before finally producing the wildtype floral whorls. In addition, silencing of AqUFO1/2 appears to specifically impact petal identity and/or the initiation of petal and stamen whorls. In general, however, there is no evidence for an essential role of AqLFY or AqUFO1/2 in transcriptional activation of the B or C gene homologs. These findings highlight differences between deeply divergent dicot lineages in the functional conservation of the floral meristem identity program.

Keywords: Aquilegia; LEAFY; UNUSUAL FLORAL ORGANS; floral meristem identity; inflorescence structure.