CmBES1 is a regulator of boundary formation in chrysanthemum ray florets

Chrysanthemum(Chrysanthemum morifolium)is an ideal model species for studying petal morphogenesis because of the diversity in the flower form across varieties;however,the molecular mechanisms underlying petal development are poorly understood.Here,we show that the brassinosteroid transcription factor BRI1-EMS-SUPPRESSOR 1(CmBES1)in chrysanthemum(C.morifolium cv.Jinba)is important for organ boundary formation because it represses organ boundary identity genes.Chrysanthemum plants overexpressing CmBES1 displayed increased fusion of the outermost ray florets due to the loss of differentiation of the two dorsal petals,which developed simultaneously with the ventral petals.RNA-seq analysis of the overexpression lines revealed potential genes and pathways involved in petal development,such as CUP-SHAPED COTYLEDON(CUC2),CYCLOIDEA 4(CYC4),genes encoding MADS-box transcription factors and homeodomain-leucine zippers(HD-Zips)and auxin pathway-related genes.This study characterizes the role of CmBES1 in ray floret development by its modulation of flower development and boundary identity genes in chrysanthemum.

The over-expression of a chrysanthemum gene encoding an RNA polymerase II CTD phosphatase-like 1 enzyme enhances tolerance to heat stress

The enzyme RNAPII CTD phosphatase-like 1 is known as a transcriptional regulator of the plant response to various abiotic stresses.Here,the isolation of CmCPL1,a chrysanthemum(Chrysanthemum morifolium)gene encoding this enzyme is described.Its predicted 955 residue gene product includes the FCPH catalytic domain,two double-stranded RNA binding motifs,and a nuclear localization signal.A sub-cellular localization assay confirmed that CmCPL1 was expressed in the nucleus.CmCPL1 transcription was shown to be significantly inducible by heat stress.The over-expression and knockdown of CmCPL1,respectively,increased and diminished the tolerance of chrysanthemum to heat stress,which maybe dependent on the regulation of CmCPL1 and on the expression of downstream heat stress-responsive genes.

Overexpression of CmSOS1 confers waterlogging tolerance in Chrysanthemum

Plants experiencing hypoxia(a shortage of oxygen)are unable to maintain aerobic respiration,which leads to an energy and carbohydrate deficit.The pervasive and rapid accumulation of ethylene is an early and reliable response to hypoxic stress(Sasidharan and Voesenek 2015),producing an uptick in the accumulation of reactive oxygen species(ROS).This in turn triggers apoptosis in root cortex cells,eventually leading to the formation of lysigenous aerenchyma,a tissue from which ethylene is readily lost(Loreti et al.2016).In plants exposed to prolonged waterlogging,group VII ethylene response factors operate to activate the suite of genes required to establish anaerobic metabolism(Gibbs et al.2011);some of these genes are also modulated by ROS(Narsai et al.2011;Sasidharan and Voesenek 2015).The transcriptional activation of genes encoding group VII ethylene response factors is regulated by the hypoxia response attenuator 1(HRA1)protein(Pucciariello and Perata 2017).A link between the oxygen sensing and ROS signaling has been established involving the hypoxia‐responsive universal stress protein 1(HRU1),which interacts with the respiratory burst oxidase homolog D(RBOHD)(Gonzali et al.2015).Salinity also tends to induce ROS production(You and Chan 2015).