A Zinc Finger Protein Regulates Flowering Time and Abiotic Stress Tolerance in Chrysanthemum by Modulating Gibberellin Biosynthesis    

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 GA 4/7 application. Under long days, changes in endogenous GA 1 , GA 4 , GA 19 , and GA 20 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.

Identification and functional characterization of the BBX24 promoter and gene from chrysanthemum in Arabidopsis

“…As in our previous work we found that CmBBX24 acts as a negative regulator in phytochrome and light signaling (Yang et al 2014). In the present investigation we examined CmBBX24 promoter activity in response to white light, blue light, red light, far-red light, and monochromatic light.…”

“…In our previous work, we isolated the full-length transcript of the BBX24 gene from young leaves of chrysanthemum and found that the gene plays an important role in abiotic stress tolerance and the flowering process in chrysanthemum (Yang et al 2014). In the present investigation, we studied the CmBBX24 promoter and found it to be very active, playing an important role in response to abiotic stress, hormones, and light treatments.…”

“…In a previous study, we determined that BBX24 protein from chrysanthemum coordinates plant responses to abiotic stress tolerance and that this process was also involved in regulating the flowering time of chrysanthemum through influencing the expression of genes related to the photoperiod pathway and the GA pathway. These results led us to speculate that the function of BBX24 in plant signaling is to act as a fine regulator of plant growth and development (Yang et al 2014). Therefore, the aim of the study reported here was to further our understanding of the regulatory mechanism of CmBBX24 expression by investigating how plant hormones, light, and abiotic stresses affect the activity of the CmBBX24 promoter and by identifying the role of the CmBBX24 promoter in the regulation of CmBBX24 in response to abiotic stresses.…”

Gibberellic Acid Signaling Is Required to Induce Flowering of Chrysanthemum Grown under Both Short and Long Days

“…The implication is that the GA pathway regulates floral induction under LD, operating via CmFTL1 SOC1 and LFY. Previous report showed that the transcript level of CmFTL3 was up-regulated specifically by GA [33], which might be due to different genetic backgroud of cultivars.…”

“…It has also been established from the behavior of A. thaliana plants grown under SD that GA induces SOC1 transcription to promote flowering [12,32]. In chrysanthemum, the loss of BBX24 (a zinc finger transcription factor) not only accelerates flowering, but also induces the photoperiod and GA synthesis pathways [33]. Meanwhile, the transcription of catabolic gene GA2ox and GAI is inhibited in WT and M plants under SD.…”