A petunia transcription factor, PhOBF1, regulates flower senescence by modulating gibberellin biosynthesis

Flower senescence is commonly enhanced by the endogenous hormone ethylene and suppressed by the gibberellins(GAs)in plants.However,the detailed mechanisms for the antagonism of these hormones during f lower senescence remain elusive.In this study,we characterized one up-regulated gene PhOBF1,belonging to the basic leucine zipper transcription factor family,in senescing petals of petunia(Petunia hybrida).Exogenous treatments with ethylene and GA3 provoked a dramatic increase in PhOBF1 transcripts.Compared with wild-type plants,PhOBF1-RNAi transgenic petunia plants exhibited shortened f lower longevity,while overexpression of PhOBF1 resulted in delayed flower senescence.Transcript abundances of two senescence-related genes PhSAG12 and PhSAG29 were higher in PhOBF1-silenced plants but lower in PhOBF1-overexpressing plants.Silencing and overexpression of PhOBF1 affected expression levels of a few genes involved in the GA biosynthesis and signaling pathways,as well as accumulation levels of bioactive GAs GA1 and GA3.Application of GA3 restored the accelerated petal senescence to normal levels in PhOBF1-RNAi transgenic petunia lines,and reduced ethylene release and transcription of three ethylene biosynthetic genes PhACO1,PhACS1,and PhACS2.Moreover,PhOBF1 was observed to specifically bind to the PhGA20ox3 promoter containing a G-box motif.Transient silencing of PhGA20ox3 in petunia plants through tobacco rattle virus-based virus-induced gene silencing method led to accelerated corolla senescence.Our results suggest that PhOBF1 functions as a negative regulator of ethylene-mediated f lower senescence by modulating the GA production.

Integrating full-length transcriptomics and metabolomics reveals the regulatory mechanisms underlying yellow pigmentation in tree peony(Paeonia suffruticosa Andr.)flowers

Tree peony(Paeonia suffruticosa Andr.)is a popular ornamental plant in China due to its showy and colorful flowers.However,yellow-colored flowers are rare in both wild species and domesticated cultivars.The molecular mechanisms underlying yellow pigmentation remain poorly understood.Here,petal tissues of two tree peony cultivars,“High Noon”(yellow flowers)and“Roufurong”(purple–red flowers),were sampled at five developmental stages(S1–S5)from early flower buds to full blooms.Five petal color indices(brightness,redness,yellowness,chroma,and hue angle)and the contents of ten different flavonoids were determined.Compared to“Roufurong,”which accumulated abundant anthocyanins at S3–S5,the yellow-colored“High Noon”displayed relatively higher contents of tetrahydroxychalcone(THC),flavones,and flavonols but no anthocyanin production.The contents of THC,flavones,and flavonols in“High Noon”peaked at S3 and dropped gradually as the flower bloomed,consistent with the color index patterns.Furthermore,RNA-seq analyses at S3 showed that structural genes such as PsC4Hs,PsDFRs,and PsUFGTs in the flavonoid biosynthesis pathway were downregulated in“High Noon,”whereas most PsFLSs,PsF3Hs,and PsF3’Hs were upregulated.Five transcription factor(TF)genes related to flavonoid biosynthesis were also upregulated in“High Noon.”One of these TFs,PsMYB111,was overexpressed in tobacco,which led to increased flavonols but decreased anthocyanins.Dual-luciferase assays further confirmed that PsMYB111 upregulated PsFLS.These results improve our understanding of yellow pigmentation in tree peony and provide a guide for future molecular-assisted breeding experiments in tree peony with novel flower colors.

PhERF2,an ethylene-responsive element binding factor,plays an essential role in waterlogging tolerance of petunia

Ethylene-responsive element binding factors(ERFs)are involved in regulation of various stress responses in plants,but their biological functions in waterlogging stress are largely unclear.In this study,we identified a petunia(Petunia×hybrida)ERF gene,PhERF2,that was significantly induced by waterlogging in wild-type(WT).To study the regulatory role of PhERF2 in waterlogging responses,transgenic petunia plants with RNAi silencing and overexpression of PhERF2 were generated.Compared with WT plants,PhERF2 silencing compromised the tolerance of petunia seedlings to waterlogging,shown as 96%mortality after 4 days waterlogging and 14 days recovery,while overexpression of PhERF2 improved the survival of seedlings subjected to waterlogging.PhERF2-RNAi lines exhibited earlier and more severe leaf chlorosis and necrosis than WT,whereas plants overexpressing PhERF2 showed promoted growth vigor under waterlogging.Chlorophyll content was dramatically lower in PhERF2-silenced plants than WT or overexpression plants.Typical characteristics of programmed cell death(PCD),DNA condensation,and moon-shaped nuclei were only observed in PhERF2-overexpressing lines but not in PhERF2-RNAi or control lines.Furthermore,transcript abundances of the alcoholic fermentation-related genes ADH1-1,ADH1-2,ADH1-3,PDC1,and PDC2 were reduced in PhERF2-silenced plants,but increased in PhERF2-overexpressing plants following exposure to 12-h waterlogging.In contrast,expression of the lactate fermentation-related gene LDH was up-regulated in PhERF2-silenced plants,but downregulated in its overexpressing plants.Moreover,PhERF2 was observed to directly bind to the ADH1-2 promoter bearing ATCTA motifs.Our results demonstrate that PhERF2 contributes to petunia waterlogging tolerance through modulation of PCD and alcoholic fermentation system.