Functional Characterization of Duplicated SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1-Like Genes in Petunia

Abstract

Flowering time is strictly controlled by a combination of internal and external signals that match seed set with favorable environmental conditions. In the model plant species Arabidopsis thaliana (Brassicaceae), many of the genes underlying development and evolution of flowering have been discovered. However, much remains unknown about how conserved the flowering gene networks are in plants with different growth habits, gene duplication histories, and distributions. Here we functionally characterize three homologs of the flowering gene SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) in the short-lived perennial Petunia hybrida (petunia, Solanaceae). Similar to A. thaliana soc1 mutants, co-silencing of duplicated petunia SOC1-like genes results in late flowering. This phenotype is most severe when all three SOC1-like genes are silenced. Furthermore, expression levels of the SOC1-like genes UNSHAVEN (UNS) and FLORAL BINDING PROTEIN 21 (FBP21), but not FBP28, are positively correlated with developmental age. In contrast to A. thaliana, petunia SOC1-like gene expression did not increase with longer photoperiods, and FBP28 transcripts were actually more abundant under short days. Despite evidence of functional redundancy, differential spatio-temporal expression data suggest that SOC1-like genes might fine-tune petunia flowering in response to photoperiod and developmental stage. This likely resulted from modification of SOC1-like gene regulatory elements following recent duplication, and is a possible mechanism to ensure flowering under both inductive and non-inductive photoperiods.

Functional and expression analyses of kiwifruitSOC1-like genes suggest that they may not have a role in the transition to flowering but may affect the duration of dormancy

“…Although SOC1 -like genes have been shown to be preferentially expressed in vegetative tissues, some are expressed in reproductive organs ( Decroocq et al , 1999 ; Heuer et al , 2001 ; Ruokolainen et al , 2011 ). Several SOC1 -like genes have been shown to be able to accelerate flowering when overexpressed ( Ferrario et al , 2004 ; Ma et al , 2011 ) or to delay flowering in mutants and upon silencing ( Lee et al , 2004 ; Preston et al , 2014 ). However, diversification of function has been observed in perennials.…”

Variation in the flowering time orthologs BrFLC and BrSOC1 in a natural population of Brassica rapa

“…The trend for the third BrSOC1 paralog was in the same direction, but was not statistically significant. It thus appears that, as in Arabidopsis (Immink et al 2012) and other species (Fu et al 2014;Lei et al 2013;Preston et al 2014), early upregulation of the BrSOC1 genes is indicative and predictive of early flowering in B.…”

Implications of region‐specific gene expression for development of the partially fused petunia corolla

“…Primers containing BamHI and XhoI recognition sequences were used to amplify target regions of 200-300 bp (Table S3, Figure S3) and cloned into the TRV2 vector cut with the same restriction enzymes. Following sequence confirmation of inserts, plasmids were transformed into Agrobacterium tumefaciens EHA105, and used with TRV1 to infect at least 30 P. hybrida plants per construct at the four to five leaf stage as previously described (Preston et al, 2014). Silencing of the anthocyanin pathway gene CHALCONE SYNTHASE (PhCHS), which causes loss of floral pigments, was used as an experimental control, also as previously described (Preston et al, 2014).…”