Molecular Mechanism Of Mung Bean Seedlings In Response To Cadmium Stress

Cadmium(Cd)is a heavy metal that can cause serious damage to plants.To respond to the detrimental effects of Cd stress,plants have to undergo a series of response mechanisms,among which physiological and biochemical mechanisms are widely studied currently,while the the molecular mechanisms are still limited.To investigate the molecular mechanism of roots,stems,and leaves in response to heavy metal,RNA-Seq technology was used in this study with mung bean as the research material and Cd,which is the most common,serious and toxic heavy metal in soil pollution,as the research object.The main results are summarized below.1.In terms of morphology,100?M Cd Cl₂ significantly inhibited the growth of shoots and roots of mung bean seedlings at 5 d and 9 d.The results showed that plant height was reduced by 25.3%and 27.5%,main root length was reduced by 20.7%and 23.4%,lateral root number was reduced by 14.5%and 34.9%,fresh weight of the ground parts was reduced by23.2%and 42.6%,and roots fresh weight was reduced by 10.8%and 57.1%at 5 and 9 d,respectively.At the same time,root distortion and serious browning were caused by Cd,which indicated that Cd stress significantly influenced the growth and development of mung bean seedlings,resulting in stunted plants and stunted root development.The results of Cd content determination showed that Cd content was 283.17 mg/kg in the roots and 18.37 mg/kg in the stems and leaves,indicating that the roots of mung bean was the main site for the accumulation of Cd.2.Transcriptome analysis of roots,stems,and leaves of mung bean exposed to Cd for 1,5,and 9 d was exployed.A total of 13055 DEGs were identified from the roots,of which the upregulated DEGs were significantly enriched in cell recognition,detoxification,secondary metabolic process,glutathione metabolic process,response to stress,toxin catabolic process,etc.,and the downregulated DEGs were significantly enriched in cell wall organization or biogenesis,microtubule-based process,anchored component of membrane,intrinsic component of plasma membrane,etc.A total of 8189 DEGs were identified from the stems,of which the upregulated DEGs were significantly enriched in cell recognition,detoxification,toxin catabolic process,secondary metabolic process,flavonoid biosynthetic process,etc.,and the downregulated DEGs were significantly enriched in cell wall polysaccharide metabolic process,cell wall organization or biogenesis,polysaccharide metabolic process,intrinsic component of membrane,integral component of membrane,etc.A total of 6705 DEGs were identified from the leaves,of which the upregulated DEGs were significantly enriched in oxidation-reduction process,regulation of endopeptidase activity,regulation of nucleic acid-templated transcription,etc.,and the downregulated DEGs were significantly enriched in microtubule-based movement,chloroplast thylakoid membrane,photosynthetic membrane,etc.3.DEGs with TPM?10 and fold change?2 were screened and analyzed.A total of7413 DEGs were obtained from roots,which included transcription factors,signaling,defense system,cell division,cell wall,and transporter related genes,suggesting that these genes played important roles in root response to Cd stress.A total of 3838 DEGs were obtained from stems.The further analysis of these DEGs showed that a large number of transporters were involved in response of stems to Cd,the genes encoding GST and POD were the key genes in stem detoxification process,and phenylpropanoid biosynthesis,flavonoid biosynthesis,tropane,piperidine and pyridine alkaloid biosynthesis,and isoquinoline alkaloid biosynthesis were the most important secondary metabolic pathway in stem response to Cd stress.A total of 2959 DEGs were obtained from leaves.The further analysis of these DEGs showed that a large number of genes related to protein synthesis and modification were differentially expressed in the middle stage of Cd stress,Cd stress significantly down-regulated photoreactive system protein genes and CO₂-fixed enzyme genes,and the key genes of the glyoxylate pathway,isocitrate lyase and malate synthase were observed to be highly differentially expressed more than 1024-fold,indicating that Cd stress significantly affected plant photosynthesis.4.Eight DEGs,including aquaporin TIP-type ecoding gene TIP,non-specific lipid-transfer protein ecoding gene SCP1,plasma membrane-associated cation-binding protein ecoding gene PCAP1,repetitive proline-rich cell wall protein ecoding gene PRP1,vacuolar-processing enzyme ecoding gene VPE,transcription factor MYB24 ecoding gene MYB24,abscisic acid receptor PYL4 ecoding gene PYL4,auxin-responsive protein IAA14ecoding gene IAA14,with known functions were selected for q RT-PCR to validate the transcriptome data.The housekeeping gene FKBP20-1 was selected as an internal reference gene for q RT-PCR measurements.The results showed that there was a strong correlation between the RNA-Seq data with q RT-PCR data(R²>0.87).TIP and PYL4 were significantly down-regulated in roots,stems,and leaves.MYB24 was significantly up-regulated in roots,stems and leaves.SCP1 was significantly up-regulated in stems and leaves.PRP1 was stably up-regulated in roots and stems,and up-regulated firstly and then down-regulated in leaves.IAA14 was down-regulated in roots and stems,and down-regulated firstly and then up-regulated in leaves.VPE and PCAP1 had different regulation patterns in different organs and at different stress stages.