| The accumulation pattern of citric acid in citrus fruits varies among different varieties.Previous studies found through transcriptomic analysis that,there are many differentially expressed genes(DEGs)in citrus fruits with significant differential citrate accumulation;however,the relationship between these genes and the differential citrate accumulation is unclear.In this study,18 genes having significant differential expressions were selected.Firstly,they were screened in citrus varieties with significantly differential citrate accumulation.Subsequently,the expression of the obtained DEGs was analyzed in the fruits of 21 citrus varieties,as well as the correlation analysis was observed between the gene expression levels and titratable acid content and pH.Finally,the genes significantly correlated with titratable acid content or pH were cloned and preliminarily verified in function.The specific results are as follows:1.Three of the 18 DEGs were found to be significantly related to titratable acid content or pHFirstly,five genes namely Ara7,XBCP3,APD2-2,U1,and U4 having higher transcription levels in high-acid citrus fruits and lower transcription levels in low-acid citrus fruits were obtained from 18 DEGs related to analyze differential citrate accumulation.Further studies on 21 citrus varieties showed that Ara7 and XBCP3 had no significant correlation with titratable acid content or pH value.U1 was significantly positively correlated with titratable acid content and negatively correlated with pH,and the Pearson correlation coefficients were 0.441 and 0.443,respectively.While,U4 and CsAPD2 were negatively correlated with pH and the Pearson correlation coefficient was 0.608 and 0.475,respectively.2.Cloning verification and preliminary functional analysis of U1A U1 gene was cloned from the citrus genome,which contained 3 exons and 2 introns.The tissue-specific analysis showed that U1 was mainly expressed in leaves,followed by juice sacs.By analyzing the expression of U1 in 6 citrus varieties with a different citric acid content,it was found that the transcription level of U1 was consistent with the changes of citric acid content,and the Pearson correlation coefficient between transcription levels of U1 and citric acid content was 0.440,reaching a significant level(p<0.05).Compared with the control group,the content of fructose and glucose increased in the callus of overexpressed U1 "Valencia orange",while,the content of citric acid decreased.Based on the above results,we can speculate that the relationship between the transcription level of U1 and the acid content in citrus fruits needs further study,and U1 may also be involved in sugar accumulation3.Cloning verification and preliminary functional analysis of U4A U4 gene was cloned from the citrus genome,which contained 8 exons and 7 introns.The tissue-specific analysis showed that U4 was mainly expressed in leaves,followed by juice sacs.By analyzing the expression of U4 in 6 citrus varieties with a different citric acid content,it was found that the transcription levels of U4 were not consistent with the changes of citric acid in lemon fruits,but consistent with that in other 5 varieties.Meanwhile,the transcription levels of U4 and citric acid content were significantly increased under drought stress.Based on the above results,we can conclude that U4 may be involved in the regulation of citric acid accumulation in citrus fruits,and the regulation of U4 on citric acid accumulation may vary from variety to variety4.Cloning verification and preliminary functional analysis of CsAPD2A homologous gene of Arabidopsis APD2 was cloned from the citrus genome(named CsAPD2).This gene contains 10 introns and 9 exons,as well as two transmembrane domains and one RING-finger domain.The tissue-specific analysis showed that CsAPD2 was mainly expressed in juice sacs.By analyzing the expression of CsAPD2 in 6 varieties with different citric acid contents,it was found that the transcription level of CsAPD2 was consistent with the changes of citric acid content,and the Pearson correlation coefficient between transcription levels of CsAPD2 and citric acid content was 0.939,reaching an extremely significant level(P<0.01).Meanwhile,the transcription levels of CsAPD2 and citric acid content were significantly increased under drought stress.Based on the above results,we can conclude that CsAPD2 is closely related to the citric acid content,and CsAPD2 may be involved in the regulation of citric acid accumulation in citrus fruits or its expression is regulated by the citric acid content. |
PDF Full Text Request