Strategies and prospects for melatonin to alleviate abiotic stress in horticultural plants

Melatonin is a conserved pleiotropic molecule in animals and plants.Melatonin is involved in many development processes and stress responses;thus,exploring its function in plants,particularly in horticultural plants,has become a rapidly developing field.Many studies have revealed that phytomelatonin acts as a plant biostimulant and increase its tolerance to various abiotic stressors,including extreme temperature,drought,osmotic disturbance,heavy metals,and ultraviolet(UV).Melatonin appears to have roles in the scavenging of reactive oxygen species(ROS)and other free radicals,affecting the primary and secondary metabolism of plants,regulating the transcripts of stress-related enzymes and transcription factors,and crosstalk with other hormones under different environmental conditions.This pleiotropy makes phytomelatonin an attractive regulator to improve resistance to abiotic stress in plants.The recent discovery of the potential phytomelatonin receptor CAND2/PMTR1 and the proposition of putative models related to the phytomelatonin signaling pathways makes phytomelatonin a new plant hormone.Based on relevant studies from our laboratory,this review summarizes the phytomelatonin biosynthetic and metabolic pathways in plants and the latest research progress on phytomelatonin in abiotic stress of horticultural plants.This study will provide a reference for elucidating the regulatory mechanism of phytomelatonin affecting the resistance to abiotic stress in plants.

The MADS-box transcription factor CmAGL11 modulates somatic embryogenesis in Chinese chestnut(Castanea mollissima Blume)

Somatic embryogenesis(SE)is an effective approach of in vitro regeneration that depends on plant cell totipotency.However,largely unknown of molecular mechanisms of SE in woody plants such as Chinese chestnut(Castanea mollissima Blume),limits the development of the woody plant industry.Here,we report the MADS-box transcription factor Cm AGL11 in Chinese chestnut.Cm AGL11 transcripts specifically accumulated in the globular embryo.Overexpression of Cm AGL11 in chestnut callus enhanced its SE capacity,and the development of somatic embryos occurred significantly faster than in the control.RNA-seq results showed that Cm AGL11 affects the expression of several genes related to the gibberellin,auxin,and ethylene pathways.Moreover,the analysis of DNA methylation status indicated that the promoter methylation plays a role in regulation of Cm AGL11 expression during SE.Our results demonstrated that Cm AGL11 plays an important role in the SE process in Chinese chestnut,possibly by regulating gibberellin,auxin,and ethylene pathways.It will help establish an efficient platform to accelerate genetic improvement and germplasm innovation in Chinese chestnut.

McMYB4 improves temperature adaptation by regulating phenylpropanoid metabolism and hormone signaling in apple

Temperature changes affect apple development and production.Phenylpropanoid metabolism and hormone signaling play a crucial role in regulating apple growth and development in response to temperature changes.Here,we found that McMYB4 is induced by treatment at 28℃ and 18℃,and McMYB4 overexpression results in flavonol and lignin accumulation in apple leaves.Yeast one-hybrid(Y1H)assays and electrophoretic mobility shift assays(EMSAs)further revealed that McMYB4 targets the promoters of the flavonol biosynthesis genes CHS and FLS and the lignin biosynthesis genes CAD and F5H.McMYB4 expression resulted in higher levels of flavonol and lignin biosynthesis in apple during growth at 28℃ and 18℃ than during growth at 23℃.At 28℃ and 18℃,McMYB4 also binds to the AUX/ARF and BRI/BIN promoters to activate gene expression,resulting in acceleration of the auxin and brassinolide signaling pathways.Taken together,our results demonstrate that McMYB4 promotes flavonol biosynthesis and brassinolide signaling,which decreases ROS contents to improve plant resistance and promotes lignin biosynthesis and auxin signaling to regulate plant growth.This study suggests that McMYB4 participates in the abiotic resistance and growth of apple in response to temperature changes by regulating phenylpropanoid metabolism and hormone signaling.

Effects of different molecular weights of chitosan on methane production and bacterial community structure in vitro

As a new feed additive,chitosan has been shown in recent years to have a certain role in reducing methane emissions from the gastrointestinal tracts of ruminants.However,the effects of chitosan with different molecular weights on rumen ferme ntation,methane production and bacterial comm unity structure are not yet clear.A basal diet without chitosa n served as the control(CTL),and the treatment diets were supplemented with chitosan with different molecular weights:1000(1K),3000(3K),5000(5K),50000(5W)and 200000(20W)dry matter(DM).Six fermentation units per treatment were established.Gas chromatography was used to measure the co nee ntrations of metha ne,H2 and volatile fatty acids(VFAs).The bacterial 16S rRNA genes were sequeneed with an Illumina MiSeq platform and analysed to reveal the relative abunda nces of bacterial community taxa.The results showed that the propi onate proporti on was sign ifica ntly in creased by the addition of chitosan with different molecular weights(P<0.05),while methane production and the acetate proportion were significantly decreased(P<0.05).The relative mbundances of Rikenellaceae_RC9_gut_group and Prevotellaceae_UCG_003 were significa ntly in creased in the 3K chitosa n group compared with the CTL group,whereas the relative abunda nee of Ruminococcaceae_NK4A214_group was significantly decreased(P<0.05).Correlation analyses of the relative abundances of the bacterial genera showed that Prevotella was positively related to propionmte production(Pv0.05).In conclusion,3K chitosan could reduce methane production by replacing fibrolytic bacteria(Firmicutes and Fibrobacteres)with amylolytic bacteria(Bacteroidetes and Proteobacteria)in the bacterial community structure.