Petal morphogenesis has a profound influence on the quality of ornamental flowers. Most current research on petal development focuses on the early developmental stage, and little is known about the late developmental stage. Previously, it was reported that the GEG gene [a gerbera homolog of the gibberellin-stimulated transcript 1 (GAST1) from tomato] negatively regulates ray petal growth during the late stage of development by inhibiting longitudinal cell expansion. To explore the molecular mechanisms of the role of GEG in petal growth inhibition, an ethylene insensitive 3-like 1 (EIL1) protein was identified from a Gerbera hybrida cDNA library by yeast one-hybrid screening. Direct binding between GhEIL1 and the GEG promoter was confirmed by electrophoretic mobility shift and dual-luciferase assays. The expression profiles of GhEIL1 and GEG were correlated during petal development, while a transient transformation assay suggested that GhEIL1 regulates GEG expression and may be involved in the inhibition of ray petal elongation and cell elongation. To study the effect of ethylene on ray petal growth, a hormone treatment assay was performed in detached ray petals. The results showed that petal elongation is limited and promoted by ACC and 1-MCP, respectively, and the expression of GhEIL1 and GEG is regulated and coordinated during this process. Taken together, our research suggests that GhEIL1 forms part of the ethylene signaling pathway and activates GEG to regulate ray petal growth during the late developmental stage in G. hybrida.

The molecular mechanism regulating petal length in flowers is not well understood. Here we used transient transformation assays to confirm that GhPRGL (proline-rich and GASA-like)—a GASA (gibberellic acid [GA] stimulated in Arabidopsis) family gene—promotes the elongation of ray petals in gerbera (Gerbera hybrida). Yeast one-hybrid screening assay identified a bHLH transcription factor of the jasmonic acid (JA) signaling pathway, here named GhBPE (BIGPETAL), which binds to the GhPRGL promoter and represses its expression, resulting in a phenotype of shortened ray petal length when GhBPE is overexpressed. Further, the joint response to JA and GA of GhBPE and GhPRGL, together with their complementary expression profiles in the early stage of petal growth, suggests a novel GhBPE-GhPRGL module that controls the size of ray petals. GhPRGL promotes ray petal elongation in its early stage especially, while GhBPE inhibits ray petal elongation particularly in the late stage by inhibiting the expression of GhPRGL. JA and GA operate in concert to regulate the expression of GhBPE and GhPRGL genes, providing a regulatory mechanism by which ray petals could grow to a fixed length in gerbera species.

14-3-3 proteins play a major role in the regulation of primary metabolism, protein transport, ion channel activity, signal transduction and biotic/abiotic stress responses. However, their involvement in petal growth and development is largely unknown. Here, we identified and characterized the expression patterns of seven genes of the 14-3-3 family in gerbera. While none of the genes showed any tissue or developmental specificity of spatiotemporal expression, all seven predicted proteins have the nine α-helices typical of 14-3-3 proteins. Following treatment with brassinolide, an endogenous brassinosteroid, the Gh14-3-3 genes displayed various response patterns; for example, Gh14-3-3b and Gh14-3-3f reached their highest expression level at early (2 h) and late (24 h) timepoints, respectively. Further study revealed that overexpression of Gh14-3-3b or Gh14-3-3f promoted cell elongation, leading to an increase in ray petal length. By contrast, silencing of Gh14-3-3b or Gh14-3-3f inhibited petal elongation, which was eliminated partly by brassinolide. Correspondingly, the expression of petal elongation-related and brassinosteroid signaling-related genes was modified in transgenic petals. Taken together, our research suggests that Gh14-3-3b and Gh14-3-3f are positive regulators of brassinosteroid-induced ray petal elongation and thus provides novel insights into the molecular mechanism of petal growth and development.

MicroRNAs (miRNAs) are involved in regulating many aspects of plant growth and development at the post-transcriptional level. Gerbera (Gerbera hybrida) is an important ornamental crop. However, the role of miRNAs in the growth and development of gerbera is still unclear. In this study, we used high-throughput sequencing to analyze the expression profiles of miRNAs in ray floret during inflorescence opening. A total of 164 miRNAs were obtained, comprising 24 conserved miRNAs and 140 novel miRNAs. Ten conserved and 15 novel miRNAs were differentially expressed during ray floret growth, and 607 differentially expressed target genes of these differentially expressed miRNAs were identified using psRNATarget. We performed a comprehensive analysis of the expression profiles of the miRNAs and their targets. The changes in expression of five miRNAs (ghy-miR156, ghy-miR164, ghy-miRn24, ghy-miRn75 and ghy-miRn133) were inversely correlated with the changes in expression of their eight target genes. The miRNA cleavage sites in candidate target gene mRNAs were determined using 5′-RLM-RACE. Several miRNA-mRNA pairs were predicted to regulate ray floret growth and anthocyanin biosynthesis. In conclusion, the results of small RNA sequencing provide valuable information to reveal the mechanisms of miRNA-mediated ray floret growth and anthocyanin accumulation in gerbera.

The CAPRICE (CPC)-like (CPL) genes belong to a single-repeat R3 MYB family, whose roles in physic nut (Jatropha curcas L.), an important energy plant, remain unclear. In this study, we identified a total of six CPL genes (JcCPL1–6) in physic nut. The JcCPL3, 4, and 6 proteins were localized mainly in the nucleus, while proteins JcCPL1, 2, and 5 were localized in both the nucleus and the cytoplasm. Ectopic overexpression of JcCPL1, 2, and 4 in Arabidopsis thaliana resulted in an increase in root hair number and decrease in trichome number. Consistent with the phenotype of reduced anthocyanin in shoots, the expression levels of anthocyanin biosynthesis genes were down-regulated in the shoots of these three transgenic A. thaliana lines. Moreover, we observed that OeJcCPL1, 2, 4 plants attained earlier leaf senescence, especially at the late developmental stage. Consistent with this, the expression levels of several senescence-associated and photosynthesis-related genes were, respectively, up-regulated and down-regulated in leaves. Taken together, our results indicate functional divergence of the six CPL proteins in physic nut. These findings also provide insight into the underlying roles of CPL transcription factors in leaf senescence.

The diversity in the petal morphology of chrysanthemums makes this species an excellent model for investigating the regulation mechanisms of petal size. However, our understanding of the molecular regulation of petal growth in chrysanthemums remains limited. The GASA (gibberellic acid [GA]-stimulated Arabidopsis) protein plays a significant role in various aspects of plant growth and development. Previous studies have indicated that GEG (a gerbera homolog of the gibberellin-stimulated transcript 1 [GAST1] from tomato) is involved in regulating ray petal growth by inhibiting cell expansion in gerberas. In this study, we successfully cloned the GASA family gene from chrysanthemums, naming it CmGEG, which shares 81.4% homology with GEG. Our spatiotemporal expression analysis revealed that CmGEG is expressed in all tissues, with the highest expression levels observed in the ray florets, particularly during the later stages of development. Through transformation experiments, we demonstrated that CmGEG inhibits petal elongation in chrysanthemums. Further observations indicated that CmGEG restricts cell elongation in the top, middle, and basal regions of the petals. To investigate the relationship between CmGEG and GA in petal growth, we conducted a hormone treatment assay using detached chrysanthemum petals. Our results showed that GA promotes petal elongation while downregulating CmGEG expression. In conclusion, the constrained growth of chrysanthemum petals may be attributed to the inhibition of cell elongation by CmGEG, a process regulated by GA.