Dynamic Process And Genetic Basis Of Rapeseed In Response To Waterlogging Occurred At Seedling Stage

Rapeseed is an important oil crop in the world,and one of main planting areas of rapeseed in China,the Yangtze River Basin,is also an area where waterlogging occurs frequently.Rapeseed is prone to waterlogging caused by soil hardening and terrible water drainage;in addition,frequent precipitation caused by meteorological changes increases the risk of rapeseed to be damaged by the waterlogging.The damage of waterlogging will lead to the loss of yield in the maturity period of rapeseed,which seriously affects its production.At present,the research on waterlogging response of rapeseed is mainly focused on the growth and physiological response during stress and growth inhibition in maturity period.In recent years,comparison of transcriptome and proteome are the main means to analyze the genetic basis of rapeseed waterlogging response.At the same time,with the wide application of the frontier technology such as genomics and phenomics in crop science,the research on waterlogging response of rapeseed also ushered in new opportunities.In this study,a Brassica napus L.natural population containing 505 inbred lines were used as research materials,and a large number of traits related to waterlogging response were obtained by manual collection and UAV phenotype platform.The dynamic changes and genetic basis of rapeseed response to the seedling waterlogging stress were analyzed using these traits,and the following results were obtained:High throughput UAV phenotype platform can collect large number of high-quality images;based on the image information,we extracted 4 morphological traits and 23spectral indices.The spectral index(NDVI)and morphological indeices(plant height and canopy volume model)were used to construct linear regression model with NDVI,plant height and biomass.The RPDs representing the performance of the three models were greater than 1.50(1.54-2.48);at the same time,the coefficients of determination of the model(R²)=0.80-0.88,MAPE=5.23%-17.96%and RMSEs are small.All the result indicates that there are high correlations between the traits extracted by UAV platform and the real values,and the UVA data precision and accuracy are very high.At the beginning of waterlogging occurred at seedling stage,the fresh weight of shoot and root decreased significantly from the 2nd day of waterlogging,and the inhibition of roots was more serious than shoot;at the same time,the blade length,blade width and petiole length of rapeseed will increase significantly within 4 days of waterlogging,but this morphological adaptive change will be gradually inhibited;the change of physiological response was consistent with the trend of morphological adaptability,but the response occurred faster and more intense.In the recovery period of waterlogging,the changes of plant height,canopy volume model and canopy cover of green leaf which reflect the growth situation,and canopy cover of purple leaf which reflect the physiological state,indicate that the inhibition of waterlogging on rapeseed growth and the physiological response of rapeseed to waterlogging will continue until the recovery period of waterlogging,and the degree of inhibition and response gradually weakens in the later recovery period.The agronomic traits at maturity stage were affected on different degrees by waterlogging stress occurred at seedling stage,of which the yield and biomass decreased the most,reaching26.8%and 27.3%respectively;waterlogging occurred at seedling stage could lead to the decrease of seed protein content and increase of oil content,but their total content was almost unchanged,indicating that waterlogging only affected the carbon source allocation in seed oil and protein synthesis,but did not affect the accumulation of energy substances.Factor analysis was carried out on the WTCs of 27 traits in 4 time point of waterlogging recovery period,and 2-5 common factors were extracted in each time point,of which still contained more than 85%of the variation in WTCs of all traits.The adaptive response of rapeseed to waterlogging mainly includes growth situation and(physiological)stress response,so the results of factor analysis only retain the first two common factors with practical significance,which were named as growth situation(GS)factor and stress response(SR)factor,respectively.Using these two common factors as phenotype traits to analyze the waterlogging tolerance of natural population of rapeseed at recovery period,it was found that the population was always clustered into three response types with obvious differences at each time point.The meteorological conditions at seedling stage will indirectly determine the seed yield at maturity stage by affecting the performance of rapeseed in response to waterlogging at seedling stage.There is a high positive correlation between precipitation at waterlogging+recovery period and WTC_SY at maturity stage(R=0.90),and a high negative correlation between solar radiation and WTC_SY at mature stage(R=-0.99).There is also a strong correlation between rapeseed traits identified at seedling stage and agronomic traits at maturity stage,then the yield-related and biomass-related traits at maturity stage can be reliably predicted by traits identified at seedling stage in the control group,waterlogging group and WTC of traits.The determination coefficient(R²)of the prediction model can reach 0.39-0.59.At the same time,the extreme materials screened by morphological traits in the recovery period of waterlogging generally have corresponding extreme performance in the maturity stage.By genome-wide association analysis(GWAS)at recovery period and maturity stage,there were identified 642 and 322 loci which related to waterlogging response.There are a large number of overlapping loci between different time points in the waterlogging recovery period,but the number of loci identified in the early stage are much more but gradually reduced in the later stage.At maturity stage,all overlapping loci were identified between highly correlated WTCs.When comparing the loci identified in different stages,we found that there was a hot spot region on A04 chromosome,which regulated the morphological traits(green leaves and PCC)at recovery period,and also related to the spectral index CIVE at recovery period and the oil content of mature seeds.Based on functional notes and significance of internal variation in genes,a gene Bna A4.DRIP2responding to abiotic stress was predicted in this region,and its negative regulation on waterlogging tolerance of rapeseed was verified by genetic transformation.Through this study,we found that UAV phenotyping platform has excellent performance in data acquisition and analysis under field conditions.The data collected by manual and UAV platform were used to analyze the rapeseed growth and physiological response dynamics to waterlogging stress at multiple stages,and the internal relationship between the performance of rapeseed under waterlogging stress at seedling stage and waterlogging tolerance formation at maturity stage was resolved.At the same time,a number of reliable loci and genes related to waterlogging tolerance response were mined,and function of a candidate gene in waterlogging response was verified.These studies can provide a theoretical basis for mitigating the effects of waterlogging in rapeseed production,and provide a theoretical basis and germplasm resources for genetic basis analysis and genetic improvement of rapeseed waterlogging response.