Preliminary Study On The Function Of S-adenosylmethionine Decarboxylase Gene (GhSAMDC1) In Cotton

Objective:Cotton is an important cash crop in China,accounting for about 21%of the world’s cotton production.Xinjiang has a long history of cotton planting,and is also the most suitable cotton planting area in China’s three major cotton areas.The four indicators of cotton planting area,unit yield,total output and output have been the first in China for 24 consecutive years.The development of cotton industry has become an important part of the people’s agricultural income in Xinjiang.However,with the emergence of a series of environmental problems,such as unreasonable use of water resources,inappropriate agricultural irrigation and warming of the climate,the abiotic stresses such as soil salinization,drought,heavy metal pollution and high and low temperatures gradually increased,which seriously affected the normal growth and development of cotton in Xinjiang and even the whole country.In recent years,with the development of biotechnology and the improvement of related technical means,cotton breeding improvement using genetic engineering technology,and the cultivation of new cotton materials with strong stress tolerance have also been developed rapidly.S-adenosylmethionine decarboxylase（SAMDC）,as one of the three key enzymes in polyamine synthesis（ADC,ODC and SAMDC）,plays an important role in regulating the synthesis and metabolism of endogenous polyamines,plant growth and development,and stress resistance.In this study,S-adenosylmethionine decarboxylase gene was cloned from upland cotton,and its basic physical and chemical properties and expression characteristics under different stress conditions were analyzed by bioinformatics and qRT-PCR.The function of GhSAMDC1 gene was analyzed by transforming Arabidopsis thaliana and tobacco,in order to regulate polyamine synthesis and metabolism and plant growth and hair by analyzing GhSAMDC1 gene.The basic principles and mechanisms of breeding and participating in the process of stress resistance provide a new theoretical basis for the study of polyamine-related functions and plant stress resistance breeding in the later stage.Methods:（1）The effect of over-expression of GhSAMDC1 on Arabidopsis seed germination under 100mmol L^-1 NaCl treatment,and the changes of endogenous free polyamines（Put,Spd and SPm）and hydrogen peroxide（H₂O₂）contents in transgenic Arabidopsis seeds during seed germination.（2）Changes of endogenous polyamines（PAs）,hydrogen peroxide（H₂O₂）,malondialdehyde（MDA）,chlorophyll content（Chl）,ion permeability（PI）,antioxidant enzymes（SOD,CAT,POD）activity and expression under salt stress in transgenic Arabidopsis thaliana seedlings treated with 100 mmol L^-1 NaCl.（3）The effects of overexpression of GhSAMDC1 on vegetative growth and reproductive growth of tobacco,and the dynamic changes of endogenous free polyamines content,polyamines synthesis and gene expression related to flowering in different growth and development stages of tobacco.Results and conclusion:（1）Seed germination of Arabidopsis thaliana（1-4,1-12,1-14）transfected with GhSAMDC1 was significantly delayed under normal culture and 100 mmol L^-1 NaCl treatment.The contents of endogenous putrescine（Put）,spermidine（Spd）,spermine（Spm）and total polyamines（PAs）in transgenic Arabidopsis thaliana treated with 100 mmol L^-1 NaCl for 1 day and 3 days were significantly lower than those in wild type.The content of endogenous hydrogen peroxide in transgenic Arabidopsis thaliana was significantly lower than that in wild type after normal cultured for 1 day.On the contrary,the content of hydrogen peroxide was significantly higher than that in wild type after treated with 100 mmol L^-1 NaCl for 3 days.Complementary experiments showed that the decrease of endogenous free Spd content in transgenic Arabidopsis thaliana might be the main reason for the delay of seed germination.（2）Overexpression of GhSAMDC1 in Arabidopsis significantly reduced the content of endogenous free putrescine（Put）and increased the content of spermidine（Spd）and spermine（Spm）.Under 100 mmol L^-1NaCl treatment,the gene expression levels of spermidine synthase（AtSPDS1,AtSPDS2）and spermine synthase（AtSPMS）were significantly increased,the content of endogenous free Spd and Spm,the content of hydrogen peroxide（H₂O₂）,MDA,Chl and ion permeability were significantly decreased.In addition,the activities of superoxide dismutase（SOD）and catalase（CAT）were significantly higher than those of wild type,and their expression levels and activity trends were changed.It is basically the same.Therefore,under100 mmol L^-1 NaCl treatment,GhSAMDC1 increased the content of endogenous free Spd and Spm in transgenic lines by increasing the expression of Spd and Spm synthesis-related genes（AtSPDS1,AtSPDS2and AtSPMS）,increased the activity of antioxidant system-related enzymes（SOD,CAT）,and enhanced the salt resistance of Arabidopsis thaliana.（3）Overexpression of GhSAMDC1 reduced the content of endogenous free Spd and increased the content of Spm.The vegetative growth of transgenic plants accelerated and flowered earlier.The expression of NtSPDS4 and NtSPMS showed the same trend as that of polyamines.The expression of flowering-related genes（NtSCO1,NtAP1,NtNFL1 and NtFT1-4）was up-regulated.External application of Spd,Spm and DCHA（polyamine inhibitors）showed that Spd and Spm were mainly involved in vegetative growth and early flowering,respectively.It is speculated that GhSAMDC1 is involved in the transformation from Spd to Spm.The decrease of Spd and the increase of Spm are the main reasons for the acceleration of vegetative growth and early flowering of tobacco.