Developmental transition and molecular basis of floral symmetry during African violet domestication
Date Issued
2012
Date
2012
Author(s)
Hsu, Hui-Ju
Abstract
Flower bilateral symmetry (zygomorphy) is among the major evolutionary trends in angiosperms as it greatly facilitates the interaction with pollinators thus creates the floral diversity. The wild type flower of the African violet (Saintpaulia sp.; Gesneriaceae) is zygomorphic, but flowers of its domesticated cultivars are mostly actinomorphic, which appears to be favoured by humans. This provides us a great opportunity to study the developmental transition between zygomorphy and actinomorphy, given their similar genetic background. Wild type flowers show zygomorphy in that two dorsal petals are samller than lateral and ventral ones and only two stamens developed in ventral parts. Two independently domesticated cultivars showed drastic differences in flower morphology: (1) Ventralized effect, Saintpaulia sp. cf. Little rick: five petals are large and equally proportionate, like the ventral petals of the wild type, and five stamens developed instead of two. (2) Dorsalized effect, Saintpaulia sp. cf. No-stamen: five petals are equally small, comparable in relative size to the dorsal petals of the wild type, and no stamens develop. It is known that the dorsally expressed flower genes CYCLOIDEA (CYC) and the its downstream gene RADIALIS (RAD) together with the ventral identity flower genes DIVARICATA (DIV) interact to create zygomorphy in Antirrhinum majus. I examined their expressions via real time PCR throughout the duration of anthesis between the wild type and two cultivars. In the wild type, SaCYC1A and SaCYC1B were expressed in dorsal petals at early stages, In contrast, in ‘No-stamen’, SaCYC1A and SaCYC1B expressed in all petals in early stages. In ‘Little rick’, we found SaCYC1A and SaCYC1B only expressed dorsally in early stages but their expression amount is less than wild type. Our results revealed that these differences became pronounced as early as the initiation of petal and stamen primordia. When correlating to SEM pictures of the flower development pattern, in ‘No stamen’ cultivar over-expression of SaCYC1A and SaCYC1B to all petals started as early as primordia initiated, this perhaps create the actinomorphic flower through the dorsalized effect. On the other hand, in ‘Little rick’, reduction of SaCYC1A and SaCYC1B expression was observed when primordia initiated, perhaps causes ventralized effect to generate the actinomorphic flower. Our results demonstrate that altering of genes in aspects of heterochrony, heterotopy and expression amount could trigger developmental transition between floral zygomorphy and actinomorphy during African violet domestications.
Subjects
zygomorphy
actinormophy
African violet
Type
thesis
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