| Chili peppers are the second biggest solanaceous vegetables after tomato in the world.Its shallow root system distribution is very vulnerable under waterlogging stress.Waterlogging stress has become one of the main abiotic stresses that limit plant growth and crop yield,and the annual loss due to waterlogging disasters exceeds one billion US dollars.However,there were few reports on the mechanisms of waterlogging tolerance in hot pepper,which requires to be investigated from multiple perspectives and levels.In this study,three hot pepper varieties(‘ZHC1’(waterlogging sensitive),‘ZHC2’(waterlogging tolerance),and ‘ZHS2’(medium waterlogging tolerance)with different waterlogging tolerance were used as tested materials.When the sixth leaf emerged,waterlogging treatments(6 h(T1)and 24 h(T2)and recovery treatments(1h(T3)and 24 h(T4)were performed,non-flooding was used as control(CK)and parameters of growth,anatomy and physiology were measured.Normal cultured materials were used as the control(CK).The differences in growth,anatomy and physiological parameters in different pepper varieties were compared under waterlogging stress and recovery conditions.In addition,two cultivars(waterloggingsensitive ‘ZHC1’ and waterlogging-tolerant ‘ZHC2’)were compared to explore the key genes and metabolic pathways that responded to waterlogging stress and recovery(T1,T2,and T3).It is helpful to explore the waterlogging-tolerant mechanisms in hot pepper,and to lay foundation for the later breeding of waterlogging-tolerant cultivars.The main results were as follows.(1)Three pepper varieties(‘ZHC1’,‘ZHC2’,and ‘ZHS2’)had significant differences in root changes at the T2 stage.Among them,the root structure of ‘ZHC2’changed significantly,the roots tended to grow on the surface of the substrate,and adventitious roots occurred at the stem base.However,the root distribution of ‘ZHC1’changed little,and some roots were rotted.The plant heights of ‘ZHC2’ and ‘ZHS2’increased by 12.75% and 12.20%,respectively,compared with the control at the T2 stage.While there was no significant changes in ‘ZHC1’.The stem diameter of the three varieties showed the most significant changes at the T2 stage.The number and size of aerenchyma at the stem base of ‘ZHC2’ were much higher than those of the other two varieties.The dry weight of ‘ZHC1’,‘ZHC2’ and ‘ZHS2’ increased by 2.00%,9.00%and-5.00% at the T2 stage,respectively,compared with the controls,among which‘ZHC2’ showed the largest increase.While ‘ZHC1’ showed decreasing trend.(2)The photosynthetic parameters of three varieties all decreased significantly under waterlogging stress.After recovery(T3 and T4 stages),different cultivars showed significant differences.‘ZHC2’ and ‘ZHS2’ recovered rapidly,while ‘ZHC1’ showed a decreasing trend.At T3 and T4 stages,the net photosynthetic rate,stomatal conductance,and transpiration rate of’ ‘ZHC1’ increased by 8.25%,-3.73% and-4.24% respectively;those of ‘ZHC2’ increased by 79.61%,43.60% and 15.99% respectively;those of ZHS2’ increased by 75.05%,19.90% and 13.56% respectively.The changes of photosynthetic pigments were consistent with the changes of photosynthetic parameters.In addition,the trend of carotenoid content among the three varieties was quite different.At the T2 stage,carotenoid content in ‘ZHC2’ increased,while that of ‘ZHC1’ and‘ZHS2’ decreased.In addition,the photosynthetic parameters had a strong correlation with growth and physiological ones by correlation analysis.(3)At the T2 stage,the contents of proline and soluble sugar in ‘ZHC2’ roots increased by 244.49% and 124.00%,respectively,compared with the control,and the increase was the most among the three varieties.Under the waterlogging stress,the amino acid content in ‘ZHC1’ root decreased by-5.46% at the T2 stage,while that of‘ZHC2’ increased by 39.28% compared with the control.The root activity of ‘ZHC2’was always significantly higher than that of ‘ZHC1’ under waterlogging stress and recovery conditions.At the T2 stage,the root activity of new adventitious roots in‘ZHC2’ was 86.40% higher than that of ‘ZHC1’.At the T2 stage,the malondialdehyde content in ‘ZHC1’,‘ZHC2’ and ‘ZHS2’ roots increased by 101.54%,21.07% and53.62%,respectively,compared with the control.The malondialdehyde content in leaves was consistent with that in roots.(4)Transcriptome analysis was performed in the roots of ‘ZHC1’and‘ZHC2’ at T1,T2,and T3 stages.A total of 15,579 differentially expressed genes(DEGs)were identified in the four comparison groups.Among them,3,384/3,642,5,090/5,923,3,177/3,438,and 4,360/5,544 up-/down-regulated DEGs were found in ZHC1-T1,ZHC1-T2,ZHC2-T1,and ZHC2-T2,respectively.Nine key DEGs related to waterlogging stress were selected for quantitative real-time PCR,and the results showed they were strong correlation with transcriptome data.The function of DEGs in response to waterlogging stress was closely related to the production of reactive oxygen species,carotenoid synthesis,auxin signal transduction,amino acid metabolism,glycolysis/gluconeogenesis,and other pathways.Some novel candidate genes related to waterlogging tolerance were also detected.The outcomes of growth and physiological analyses were consistent with the transcriptome data.This work provides new insights into waterlogging-tolerant mechanisms and valuable clues for breeding of waterlogging-tolerant pepper. |
