Symmetry genes and shifts in corolla bilateral symmetry

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Repeated losses of mature corolla bilateral symmetry are not uncommon. Zhong et al. focus on repeated and diverse losses of bilateral symmetry testing whether similar or distinct developmental genetic mechanisms underlie shifts in corolla symmetry in Lamiaceae.

Ontogenetic origins of mature radially symmetrical corollas

Ontogenetic origins of mature radially symmetrical corollas in (A–E) Mimulus guttatus, (F–J) Callicarpa cathayana, (K–O) Lycopus americanus and (P–T) Mentha longifolia. Cartoons (E), (J), (O) and (T) depict mature developmental stages for four focal species. Mimulus corollas are bilaterally symmetrical with five petals from early (B–D) to late (E) developmental stages; Callicarpa corollas are tetramerous and radially symmetrical from petal initiation to late development (G–I); corollas of Lycopus (L–N) and Mentha (P) are initially pentamerous and bilaterally symmetrical with two adaxial petals being fused during development (Lycopus, M, N; Mentha, Q, R), and the final corolla forms become tetramerous and radially symmetrical (Lycopus, O; Mentha, S, T). However, Lycopus has only two adaxial fertile stamens (yellow) with the other two abaxial (green) being sterile (O), while Menthahas four fertile stamens (yellow) (T); all species have two carpels (centre, blue). Scale bars = 50 μm except (I) = 100 μm and (S) = 200 μm. Sepal, s; petal, p; stamen, st; gynoecium, g; adaxial sepal, ds; abaxial sepal, bs; lateral sepal, ls; adaxial petal, dp; abaxial petal, bp; lateral petal, lp; lateral stamen, lst; abaxial stame

Using phylogenetic, SEM-based developmental and gene expression analyses, repeated losses of mature corolla bilateral symmetry in Lamiaceae are shown to result from various different mechanisms and changes to symmetry genes, including losses of a CYC2 clade and a RAD-like gene from the genome.

Reference

Zhong, J., Preston, J. C., Hileman, L. C., & Kellogg, E. A. (2017). Repeated and diverse losses of corolla bilateral symmetry in the Lamiaceae. Annals of Botany, 119(7), 1211–1223. https://doi.org/10.1093/aob/mcx012


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