Abstract
Flowering time and an ability to tolerate abiotic stresses are important for plant growth and development. We characterized BBX24, a zinc finger transcription factor gene, from Chrysanthemum morifolium and found it to be associated with both flowering time and stress tolerance. Transgenic lines with suppressed expression of Cm-BBX24 (Cm-BBX24-RNAi) flowered earlier than wild-type plants and showed decreased tolerance to freezing and drought stresses. Global expression analysis revealed that genes associated with both photoperiod and gibberellin (GA) biosynthesis pathways were upregulated in Cm-BBX24-RNAi lines, relative to the wild type. By contrast, genes that were upregulated in overexpressing lines (Cm-BBX24-OX), but downregulated in Cm-BBX24-RNAi lines (both relative to the wild type), included genes related to compatible solutes and carbohydrate metabolism, both of which are associated with abiotic stress. Cm-BBX24 expression was also influenced by daylength and GA4/7 application. Under long days, changes in endogenous GA1, GA4, GA19, and GA20 levels occurred in young leaves of transgenic lines, relative to the wild type. Regulation of flowering involves the FLOWERING TIME gene, which integrates photoperiod and GA biosynthesis pathways. We postulate that Cm-BBX24 plays a dual role, modulating both flowering time and abiotic stress tolerance in chrysanthemum, at least in part by influencing GA biosynthesis.
Highlights
Flowering at the appropriate time of year is essential for successful reproduction and has commercial significance for crops and ornamental plants
Plants have been shown to utilize various and often interconnecting flowering mechanisms, including photoperiod, vernalization, gibberellin (GA) biosynthesis, and aging pathways (Song et al, 2013). Outputs from these pathways are integrated by a set of common downstream flowering-time integrators, such as FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CO1 (SOC1), whose expression leads to the induction of floral meristem identity genes, including LEAFY (LFY) and APETALA1 and, flowering (Song et al, 2013)
Phylogenetic analysis of BBX proteins from a range of plant species revealed the predicted protein to cluster with structure group IV BBX homologs from Arabidopsis and that this gene is a homolog of At-BBX24 and At-BBX25 (Figure 1B), with the greatest similarity to At-BBX24
Summary
Flowering at the appropriate time of year is essential for successful reproduction and has commercial significance for crops and ornamental plants. Plants have been shown to utilize various and often interconnecting flowering mechanisms, including photoperiod, vernalization, gibberellin (GA) biosynthesis, and aging pathways (Song et al, 2013). Outputs from these pathways are integrated by a set of common downstream flowering-time integrators, such as FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CO1 (SOC1), whose expression leads to the induction of floral meristem identity genes, including LEAFY (LFY) and APETALA1 and, flowering (Song et al, 2013).
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