Physiological And Molecular Mechanisms Of Exogenous Thiamine Alleviating Drought Stress In Pterocarya Stenoptera

Pterocarya stenoptera C.DC.is a genus of the Pterocarya in the Juglandaceae family.It has good ornamental value and is often used for landscaping planting.P.stenoptera is often affected by drought stress during growth due to urban heat island effect,highly hardened road surfaces and changes in soil physicochemical properties,resulting in dehydration and yellowing of leaf edges,which affects their normal growth and landscape greening effect.Previous reverse transcriptomic studies have shown that thiamine synthesis genes THI1 and THIC are responsive to drought stress in P.stenoptera.Therefore,it is speculated that thiamine may play an important role in drought stress in P.stenoptera.In this experiment,the effect of external application of thiamine on the morphology and growth of P.stenoptera under drought stress was investigated to screen the appropriate thiamine treatment concentrations.The effects of exogenous thiamine on the physiological indicators and transcriptome of P.stenoptera under drought stress were further investigated using the screened appropriate concentrations,and a combined physiological and transcriptomic approach was used to elucidate the molecular regulatory mechanisms behind the alleviation of drought stress in P.stenoptera by exogenous thiamine.The main results are as follows:1.Drought stress significantly inhibited seedling growth of P.stenoptera.However,pretreatment with 10 m M thiamine could effectively alleviate the inhibition of plant height growth by drought stress,reduce the drying rate of leaves,and enhance drought resistance of P.stenoptera.2.Drought stress significantly reduced the content of chlorophyll a and chlorophyll b.Exogenous thiamine maintained the high expression level of chlorophyll synthesis genes under drought stress,thus maintaining the high contents of chlorophyll a and chlorophyll b,keeping the green color of leaves,and reducing the effects of drought stress on leaves.3.Under drought stress environment,P.stenoptera were photoinhibited.The application of exogenous thiamine could protect the PSⅡ reaction center of P.stenoptera.High content of chlorophyll also maintained the expression of photosynthesis genes under drought stress,thus reducing the effect of drought stress on photosynthesis.4.By transcriptome sequencing analysis that the expression levels of eight chlorophyll synthesis genes were significantly higher in P.stenoptera with thiamine pretreatment than in those with water pretreatment under drought stress as analyzed by transcriptome sequencing.Exogenous thiamine supplementation also activated the expression of the genes in auxin-activated signaling pathway under drought stress.High expression level of the genes in auxin-activated signaling pathway might also be one of the factors that reduce the effects of drought stress on P.stenoptera.Additionally in this study,the results indicated that exogenous thiamine did not affect the synthesis of endogenous thiamine,but increased the thiamine metabolic burden in P.stenoptera.In conclusion,exogenous thiamine improved the drought resistance of P.stenoptera and effectively alleviated plant damage caused by drought stress.This study provides a typical example for non-model woody plants lacking transgenic systems and provides an effective method to mitigate the effects of drought stress on plants.