Study On The Physiological Dynamics And Comparative Transcriptome Analysis Of Different Cadmium Accumulation Rice Varieties

Backgroud:Rice（Oryza sativa L.）is the main food crop worldwide.Recently,the forms“cadmium rice”,which due to its characteristic of enriching cadmium from soil to grains and other organs,inducing serious dangers to human health.Objective:Therefore,in this study,we selected the varieties of high grain-cadmium accumulation‘Yuzhenxiang’（YZX）and low grain-cadmium accumulation‘Xiangwanxian 12’（XWX）as experiment materials to compare analysis of the physiological changes and the underlying molecular mechanisms under different Cd-polluted environmental conditions.Methods and Results:1.Firstly,we comparison testifying the 89 rice cultivars in the soil with Cd content of 1.60 mg/kg,the results showed that the variation of cadmium accumulation in rice was mainly caused by genotypic difference but not the environmental factors.Then,we have identified 10cultivars consistent with their Cd content selected on four low cadmium loci（q Cd7.1,q Cd7.2,q Cd2,and q Cd11）.Such as,Xiangwanxian 12,Neixianghongyou 13,Honghuanghong,D you35,Bijing43,Chengyou 33,Jinyou 785,Tianlongyou 1188,Yixiang 725,and Dalixiang.Therefore,we used XWX and YZX as experiment materials because of their representative in field phenotypic accumulated cadmium and low cadmium loci.2.Secondly,we compare analysis of the cadmium contents,in different organs（roots,stems,sheaths and leaves,grains）at four growth stages（tillering stage,booting stage,full heading stage,mature stage）,and then testified the photosynthetic parameters and antioxidant enzyme activities of leaves.The results are showing below:With the increase of Cd concentration in soil,the Cd content in rice organs gradually increased.The Cd content in four growth stages of rice plant from high to low was as following:tillering stage>booting stage>full heading stage>mature stage.The Cd content of rice organs in the mature stage from high to low as following:roots>stems>sheaths and leaves>grains.And the Cd content in all organs of XWX grain was significantly lower than that of YZX.The Photosynthetic rate（Pn）,stomatal conductance（Gs）,intercellular CO₂concentration（Ci）,and transpiration rate（Tr）of Xiangwanxian 12 were all significantly higher than those of Yuzhenxiang.The enzyme activities of superoxide dismutase（SOD）,peroxidase（POD）,and catalase（CAT）of XWX was higher than that of YZX,but the malondialdehyde（MDA）content was lower than that of Yuzhenxiang.With the increase of Cd concentration in soil,the activities of SOD,POD,and CAT of the two tested cultivars increased gradually,while MDA content was decreased gradually.3.Thirdly,we set four growth and development stages to add exogenous cadmium for stress under the condition of hydroponics during the whole growth period compared at three temperature gradients.Then the Cd content in each organ of rice was measured every 24 h for 6consecutive days.The results showed that the cadmium content in each organ from high to low was:roots>stems>sheaths and leaves>grains.In the growth and development stage of rice,the Cd content in leaves from high to low is:tillering stage>booting stage>full heading stage>mature stage.4.Lastly,we compare analysis the root system of YZX and XWX was treated with 2 mg/L cadmium stress for 48h at booting stage at medium temperature condition（22～27℃）:RNA-seq results showed that 341 and 161 transcripts were differentially expressed after Cd treatment in YZX and XWX,respectively.These genes might be potential Cd responsive genes in YZX and XWX.The interaction network analysis of these abnormal transcripts in YZX or XWX after cadmium stress was established by using STRING database,we noticed that there were seven genes that may play an important role in cadmium response were screened according to the number of adjacent genes in the interaction network.We identified 41 cadmium-related genes by GO annotation analysis.A total of 257 transcripts that might be related to the difference in Cd uptake capacity between YZX and XWX roots were screened.ADI1、CFBP1、p EX11-4、Os J＿019618、Os J＿24808、GDCSH、CLPB1 and WNK3 may play important roles in cadmium response and tolerance.Conclusion:Above all,we have identified ten rice varieties with lower Cd accumulation ability.Our results showed that there was significant difference of Cd content in plant roots at booting stage between YZX and XWX under medium temperature（22～27℃）.Moreover,our research indicated that ADI1、CFBP1、p EX11-4、Os J＿019618、Os J＿24808、GDCSH、CLPB1 and WNK3 genes may play important roles in cadmium response and tolerance.