Mechanism Of Plant Defensin PDF2.1 Regulating Ammonium Metabolism And Cadmium Tolerance

Plant defensins are small peptides rich in cysteine.In Arabidopsis thaliana,plant defensins are divided into two families:PDF1s and PDF2s.Previous studies have shown that AtPDF1.1 is involved in the response of plants to biological stress.Other studies have found that PDF1s improves zinc tolerance in plants and yeast.To our knowledge,the molecular mechanism of PDF2.1 in Arabidopsis thaliana has not been elucidated.We found that PDF2.1 was induced by ammonium and cadmium in Arabidopsis thaliana.However,how PDF2.1 regulates plant ammonium metabolism and plant tolerance to cadmium is unclear.In this study,we studied the effects of PDF2.1 on the ammonium metabolism of Arabidopsis thaliana under normal culture conditions and under 10?m Cd Cl₂stress by using wild type Col-0 and mutants pdf2.1-1 and pdf2.1-2 as materials.The main results are as follows:1.AtPDF2.1 affects ammonium metabolism by regulating the expression of GLN1.3 and GLN1.5.In plants,ammonium metabolism is particularly important for converting absorbed nitrogen into amino acids.However,the molecular mechanism underlying this conversion remains largely unknown.Using wild type Arabidopsis thaliana(Col-0)and AtPDF2.1mutants(pdf2.1-1 and pdf2.1-2),we found that AtPDF2.1 is involved in regulating ammonium metabolism in the shoot.Ammonium significantly induced the expression of AtPDF2.1 in the shoot and root,particularly in root xylem vascular bundles,as demonstrated by histochemical analysis.Subcellular localization analysis revealed that AtPDF2.1 was localized to the cell wall.Ammonium concentration was higher in the shoot of mutants than in the shoot of Col-0,but no differences were found for total nitrogen content,root ammonium concentration,and the expression of the ammonium transporter gene AtAMT2.1.The activity of glutamine synthetase was significantly decreased in mutants,and the glutamine synthetase family genes GLN1.3 and GLN1.5 were significantly downregulated in mutants compared to Col-0.The activity of nitrate reductase showed no difference between mutants and Col-0.Overall,these data suggest that AtPDF2.1 affects ammonium metabolism by regulating the expression of GLN1.3 and GLN1.5 through a yet unidentified mechanism.2.Loss of AtPDF2.1 function makes Arabidopsis thaliana more sensitive to cadmium stress.After cadmium treatment,the leaves of the mutants were yellowed more seriously,the chlorophyll concentration was lower,and the proline concentration of wild-type roots was significantly higher than that of the mutants.These phenomena indicate that plants become more sensitive after PDF2.1 mutation in Arabidopsis thaliana.The concentration of Cd in the shoot of mutants were significantly higher than that in wild type,the difference between wild type and mutants were not significant in roots,and the concentration of Cd in the xylem of mutants were also significantly higher than that in wild type,and the expression of IRT1 and ZIP1 genes in mutants were significantly higher than that in wild type,which indicated that mutants absorbed more Cd and transported Cd to shoots.In Arabidopsis thaliana,the expression of HMA2 in mutants were significantly lower than wild type,and the activity of SOD in mutants were significantly higher than wild type.In general,after PDF2.1 mutation,Arabidopsis thaliana absorbs more cadmium and transports it to shoots,which weakens the plant's resistance to Cd stress,but the specific molecular mechanism needs further study.