Abstract
Gerbera hybrida is a cut-flower crop of global importance, and an understanding of the mechanisms underlying petal development is vital for the continued commercial development of this plant species. Brassinosteroids (BRs), a class of phytohormones, are known to play a major role in cell expansion, but their effect on petal growth in G. hybrida is largely unexplored. In this study, we found that the brassinolide (BL), the most active BR, promotes petal growth by lengthening cells in the middle and basal regions of petals, and that this effect on petal growth was greater than that of gibberellin (GA). The RNA-seq (high-throughput cDNA sequencing) technique was employed to investigate the regulatory mechanisms by which BRs control petal growth. A global transcriptome analysis of the response to BRs in petals was conducted and target genes regulated by BR were identified. These differentially expressed genes (DEGs) include various transcription factors (TFs) that were activated during the early stage (0.5 h) of BL treatment, as well as cell wall proteins whose expression was regulated at a late stage (10 h). BR-responsive DEGs are involved in multiple plant hormone signal pathways, hormone biosynthesis and biotic and abiotic stress responses, showing that the regulation of petal growth by BRs is a complex network of processes. Thus, our study provides new insights at the transcriptional level into the molecular mechanisms of BR regulation of petal growth in G. hybrida.
Highlights
Brassinosteroids (BRs) are plant-specific steroid hormones involved in many growth and developmental processes, such as cell division and elongation, leaf expansion, vascular differentiation, stress tolerance, senescence and stomatal development (Bajguz & Hayat, 2009; Clouse & Sasse, 1998; Gudesblat et al, 2012; Kim et al, 2012)
Because GAs and BRs coordinately regulate plant growth in Arabidopsis (Li et al, 2012), and GAs promotes petal elongation in G. hybrida (Li et al, 2015), we tested the effect of combined treatment with GA3 and BL on petal growth in G. hybrida
ARL, a gene controlling cell expansion during organogenesis, acts downstream of Figure 6 (...continued) (D) differentially expressed genes (DEGs) selected from the four classes (E) Nine DEGs selected randomly
Summary
Brassinosteroids (BRs) are plant-specific steroid hormones involved in many growth and developmental processes, such as cell division and elongation, leaf expansion, vascular differentiation, stress tolerance, senescence and stomatal development (Bajguz & Hayat, 2009; Clouse & Sasse, 1998; Gudesblat et al, 2012; Kim et al, 2012). Large-scale analysis using microarray or proteomic techniques has demonstrated the importance of BR-regulated genes in cell expansion. These genes are involved in cell wall modification, cellulose biosynthesis, ion and water transport, and cytoskeleton rearrangement (Clouse & Sasse, 1998; Kim & Wang, 2010; Vert et al, 2005). Further studies in Arabidopsis showed that BRASSINAZOLERESISTANT1 (BZR1) and BRI1-EMS-SUPPRESSOR1 (BES1) encode two major transcription factors (TFs) that regulate cell division and elongation through a large number of BR -responsive genes (Guo et al, 2009; He et al, 2005; Sun et al, 2010; Wang et al, 2002; Xie, Yang & Wang, 2011; Yin et al, 2002; Yu et al, 2011)
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