METHODS: Phylogenetic analysis was used to identify candidate Dendrobium catenatum R2R3-MYB (DcaMYB) sequences associated with pigment and cell shape development. Gene silencing of candidate DhMYBs in Dendrobium hybrid by direct application of dsRNA to developing flowers was followed by observation of gene expression level and flower phenotypes. Silencing of the structural gene chalcone synthase was used as a comparative control.
KEY RESULTS: Ten candidate flower-associated DcaMYBs were identified. Flowers treated with dsRNA of DhMYB22 and DhMYB60 sequences were less pigmented and had relatively low expression of anthocyanin biosynthetic genes (F3'H and DFR), lower total anthocyanin concentration and markedly lower levels of cyanidin-3-glucoside and cyanidin-3-rutinoside. Petals of DhMYB22-treated flowers and sepals of DhMYB60-treated flowers showed the greatest colour difference relative to the same organs in untreated flowers. DhMYB22-treated flowers had relatively narrow and constricted lips, while DhMYB60-treated flowers had narrow and constricted sepals. No significant difference in shape was observed for DhCHS-treated or untreated flowers.
CONCLUSIONS: Our results demonstrate that DhMYB22 and DhMYB60 regulate pigment intensity and floral organ shape in Dendrobium. This is a first report of MYB regulation of floral organ shape in orchids.
SCOPE: For this review, we analysed recent research publications reporting specifically on plant transcription factor (TF) expression in association with PGPB, to determine if there are any common findings and to identify gaps that offer opportunities for focused future research.
CONCLUSIONS: The inoculation of plants with PGPB elicits a dynamic and temporal response. Initially, there is an upregulation of defence-responsive TFs, followed by their downregulation in an intermediate phase, and finally, another upregulation, providing longer term stress tolerance. PGPB priming activates plant defences in the form of induced systemic resistance (ISR), often via the MAMP/MAPK pathways and involving one or more of the major plant hormone-signalling pathways and their crosstalk. Following PGPB priming, the TF families most commonly reported as expressed across different plants and for different pathogens are ERF and WRKY, while the TFs most commonly expressed across different plants for different abiotic stresses are ERF and DREB. There were inconsistencies between studies regarding the timing of the shift from the initial phase to the intermediate phase, and some of the TFs expressed during this process have not been fully characterized. This calls for more research to investigate the regulatory functions and phases of TF expression, to enhance crop resilience. Most reports on abiotic stresses have focused on salinity and drought, with fewer studies addressing nutrient deficiency, heavy metals, flooding and other stresses, highlighting the need for further research in these areas.