Molecular Mechanism Of Strigolactons In The Regulation Of Drought And Salt Resistance In The S.sebiferum

S.sebiferum is an economic forest tree species that integrates various uses such as ornamental,energy,medicinal and timber materials.It has a strong resistance to drought,salt,and alkali.Plants have evolved the ability to adapt to various adversities by regulating their growth indicators,hormone levels and the expression of stress-related genes.Therefore,hormones play a vital role in the alleviation of abiotic stress tolerance.Strigolactone(SL)is a newly discovered plant hormone with many biological functions.Recently,it has been found that strigolactone is involved in the regulation of plant stress responses.MAX2 is a key gene involved in the signal transduction of strigolactone in Arabidopsis.The mutant of Atmax2 is susceptible to abiotic stress,but the mechanism of regulation remains unclear,especially in woody plants.In this study,we explored the effects of exogenous strigolactone on the stress response of S.sebiferum seedlings under drought and salt stress,we also explored the molecular functions of SsMAX2 in the regulation of the stress adaptation.The main results of this study were as follows:Exogenous strigolactone on the regulation of stress adaptation in the S.sebiferum seedlings.Under mild stresses,mannitol and NaCl(50 mM),the seed germination rate,and the dry weight of S.sebiferum seedlings were induced.These results indicated that mild stress stimulated osmotic adjustment and promoted various organic and inorganic substances in the S.sebiferum seed and seedlings.Under severe stress,50 nM SL was applied to induce the drought and salt stress tolerance in S.sebiferum seedlings and increase the seedlings biomass.SL induced the proline(Pro)content and enhanced the activity of SOD,POD and CAT by regulating the oxidation system in S.sebiferum seedlings.The enhanced activity of antioxidants could improve the ability of S.sebiferum seedlings to scavenge free radicals and peroxides,reduce the damage of free radicals and peroxides in the cell membrane,and improve the stress resistance in the S.sebiferum seedlings.SsMAX2 gene analysis.Bioinformatic analysis of the full length and amino acid alignment of the SsMAX2 gene sequence showed that S.sebiferum has a very close evolutionary relationship with the Ricinus communis as both belong to the euphorbiaceae family.MAX2 encodes the F-box Protein,which is involved in the transmission of various hormonal signals of ethylene,GA and auxin,and studies have shown that it may be involved in jasmonic acid and abscisic acid.These results suggested that SsMAX2,a key signal transduction gene for strigolactone,responds to plant abiotic stress by regulating plant branching,seed germination,and functions in response to multiple hormones.This study Provides a theoretical basis for directional cultivation of imProved S.sebiferum varieties.Overexpression of SsMAX2 in Arabidopsis improved the drought and salinity stress tolerance.The germination rate of SsMAX2 Arabidopsis seeds in drought and salt stress was over 50%;SsMAX2 seedlings also showed resistant to drought and salt stresses.Drought and salt treatment significantly induced hydrogen peroxide in Arabidopsis seedlings.The accumulation of hydrogen peroxide in the SsMAX2 Arabidopsis was significantly lower than that of the max2 mutant and wild-type(WT).The higher activity of antioxidants such as CAT,POD and SOD also showed that SsMAX2 Arabidopsis had higher hydrogen peroxide decomposition ability under salt stress and drought stress,while max2 mutant showed lower enzyme activity.These results reveal that the SL signal may be directly involved in the regulation of redox homoestasis.The study found that under drought conditions,SsMAX2 also regulates the synthesis and accumulation of anthocyanins,and participates in the synthesis of chlorophyll under salt stress conditions.This study provides a new foundation for studying SL's participation in plant stress resistance.(4)Preliminary revealing the regulation mechanism of SsMAX2 involved in the resistance of S.sebiferum.The relationship between the expression level of SsMAX2 and ABA-synthesizing genes under Arabidopsis stress conditions was demonstrated.The SL signal transduction gene SsMAX2 was involved in the synthesis and degradation of chlorophyll,anthocyanin biosynthesis,and accumulation of TSS and Proline.Physiological and biochemical results indicated that SsMAX2 regulated redox homeostasis by regulating antioxidant enzymes.It was also found that there may be interactions between SL and ABA in abiotic stress adaptation,revealing the regulation of exogenous SL regulating the stress resistance of S.sebiferum seedlings.The mechanism provides a new way for the study of SL in S.sebiferum and has a significant theoretical and practical value in improving the ability of plants to adapt the drought and salt stresses.