Transcriptomics-Based Analysis of Pepper Responses to Phosphorus Nutritional Stress
[Objective]This study aimed to explore the changes in the transcriptional level and physiological responses of pepper(Capsicum annuum L.)seedlings under different phosphorus stress gradients,to analyze the key pathways,and to integrate related experiments to elucidate the physiological mechanisms of the pepper response to nutritional stress of phosphorus.This study also identified the transcription factors and core genes that regulate the nutritional stress of phosphorus,so as to provide a theoretical basis and genetic resources for the breeding of peppers.[Method]This study used the roots of the pure CA#8 seedlings of pepper as experimental material,grown by Hoagland hydroponics in a single four-leaf stage and subjected to four different gradient phosphorus stress treatments,namely control group(CK,200 μmol·L-1 NH4H2PO4)and phosphorus deficiency group(DP,0 μmol·L-1 NH4H2PO4),low phosphorus stress group(LP,20 μmol·L-1 NH4H2PO4),and high phosphorus stress group(HP,1 000 μmol·L-1 NH4H2PO4).Transcriptome sequencing(RNA-Seq)was performed on pepper roots systems 2 days after treatment,and the endogenous hormone levels and antioxidant enzyme activities were measured after 0,2,4,and 6 days of treatment,respectively.[Result]Compared with the CK group,the DP,LP,and HP groups exhibited 626,107,and 171 differentially expressed genes(DEG),respectively.10 DEGs related to the phosphorus signaling pathway,4 DEGs related to the plant hormone signal transduction pathway,and 7 DEGs related to antioxidant enzyme activities were identified by GO,KEGG enrichment analysis,and WGCNA analysis.Real-time fluorescence quantitative(qRT-PCR)was used to validate the accuracy of transcriptome data.Quantitative measurements of endogenous hormones in the roots of pepper seedlings showed that with increasing duration phosphorus stress,the levels of various growth-promoting endogenous hormones such as gibberellin(GA),brassinolide(BR),cytokinin(CTK),indole acetic acid(IAA),strigolactone(SL),and jasmonic acid(JA)decreased in the DP,LP and HP groups,while the levels of growth-inhibiting hormones such as ethylene(ETH)and abscisic acid(ABA)increased,especially under phosphorus deficiency and low phosphorus stress,where growth inhibition of the seedling roots was the most significant.Various phosphorus stress-induced increased activities of superoxide dismutase(SOD),peroxidase(POD),and catalase(CAT)in pepper root tissue,while the activities of SOD decreased at the later stage of stress,and POD and CAT tended to be stable too.[Conclusion]During various phosphorus nutritional stress,the pepper seedlings mitigated the effects of phosphorus stress on growth by responding to phosphorus signaling pathways,plant hormone signal transduction pathways,and differentially expressed genes related to antioxidant enzyme activity,thus improving the tolerance to phosphorus stress of pepper seedlings.
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