Study On Physiological And Molecular Mechanisms Of Differences Between Potato Varieties And Organ Cadmium Accumulation

Cadmium(Cd)pollution was a global environmental problem.Cadmium entered the human body through bioaccumulation,posing a threat to human health.Potato(solanum tuberosum L.)is an important staple food crop in the world,and it is urgent to reduce the cadmium accumulated in the potato to avoid the harm of cadmium pollution to the human body.Planting crops in cadmium-contaminated areas,especially in southern acidic soils,can easily aggravate the risk of cadmium exceeding the standard.Therefore,before cadmium pollution is completely eradicated,planting potato varieties with low cadmium accumulation is the most economical and effective way to avoid the risk of cadmium pollution.However,there are relatively few studies on the low accumulation mechanism of cadmium in potatoes.This paper compared the differences in cadmium accumulation in the tubers of 28 potato varieties under the treatment of cadmium polluted field environment,and then screened potato varieties with high and low cadmium accumulation in tubers,and analyzed the characteristics of cadmium accumulation and distribution among different organs of potato using transcriptome.To analyze the differences in cadmium accumulation in different organs of potato and the physiological and molecular mechanisms of potato in response to cadmium stress by transcriptome and micro RNA sequence,and screened and obtained relevant key genes for cadmium accumulation and stress response.On this basis,the functions of key transporter genes were initially identified,and found to allelic variants.This study will provide strong support for the safe production of cadmium accumulation in potato varieties.The main results were as follows:(1)Selection of potato varieties with low cadmium accumulation and the law of cadmium accumulation and distribution.Through many years of comparative experiments of varieties under lightly and severely polluted cadmium fields,the potato varieties “Huashu4” and “Eshu10” with high and low cadmium accumulation were selected.By analyzing the characteristics of accumulation in the three organs of potato leaves,stems and tubers,it was found that the cadmium content rule was leaf>stem>tubes,and the cadmium accumulation in stems and leaves accounted for more than 80% of the total plant.In addition,the potato “Eshu10” can be used for phytoremediation of cadmium-contaminated soil,and it can also produce low-cadmium tubers that are safe for consumption.(2)Physiological and molecular mechanisms of potato in response to cadmium stress.The pot experiment results of different cadmium stress treatments showed that the roots of the organs had the highest cadmium content,and the tubers had the lowest cadmium content.The cadmium content of each organ increased with the soil cadmium concentration,with the increase of cadmium concentration,the plant height and leaf SPAD value,Net photosynthetic rate showed a downward trend;Proline(Pro),malondialdehyde(MDA),Catalase(CAT),superoxide unmutes(SOD)and grains in potato cells under cadmium stress treatment.The content of antioxidants such as non-protein thiol(NPT)increases rapidly,and the antioxidant enzyme system catalase(CAT)and superoxide unmutes(SOD)were activated and maintain a certain level of activity to remove the cell’s reactive oxygen species damage.Transcriptome and micro RNA sequence and analysis of the roots,leaves and tubers of plants treated with different concentrations of cadmium stress showed that photosynthesis,phenyl acetone biosynthesis,glutathione metabolism,plant hormone signal transduction,MAPK signaling pathway,Terpenoid biosynthesis and starch and sucrose metabolism,these pathways played an important role in the response of different potato tissues to cadmium stress.The 19 genes,for example,St HMA3-like(LOC102604572),St Nramp5-like(LOC102584518)and St HMA1-like(LOC102602884),which were key genes for cadmium accumulation in potato tubers,leaves and roots,and were differentially expressed under cadmium stress.Through mi RNA-m RNA association analysis,the mechanism of potato response to cadmium stress was explored.As a result,a large number of candidate mi RNAs and m RNAs were obtained.At the same time,under the treatment of cadmium stress,multiple mi RNAs were significantly expressed in the tubers,roots and leaves of different organs of potato.The target of stu-mi R5303 e was LOC102602058,which encoded Nramp2 transporter(Metal transporter Nramp2-like),which was closely related to the transport of metal divalent cations.The target of stu-mi R5303 h was LOC102598735,and its expression was down-regulated under cadmium stress.This gene belongs to a large gene family(Trichome Birefringen-Like,TBL)that was unique to plants and was mainly involved in the acetylation modification of non-fibrous polysaccharides.The target gene of stu-mi R5303 h was LOC102594095,and its encoded protein was pleiotropic drug resistance protein 2-like(PDR),which was a common heavy metal efflux protein that can enter plant cells through the rhizosphere.The cell membrane was transported out of the cell to reduce the toxicity of heavy metals to plant cells;the target gene of stu-mi R172c-3p was LOC102589826,which is down-regulated under cadmium stress.AP2-like ERF(Ethylene-responsive factor)encoded by the target gene is a type of ethylene-responsive transcription factor with AP2 domain characteristics,and played a key role in responding to plant stress responses.(3)Study on the function of HMA(Heavy metal ATPase)gene family in cultivars with high and low accumulation of cadmium.The pot experiment results of the cadmium high accumulation variety “Huashu4” and the low cadmium accumulation variety “Eshu10” under different concentrations of cadmium stress showed that the plant height,leaf SPAD,and net photosynthetic rate of the two varieties all increased with the cadmium concentration.The increase showed a downward trend,and the cadmium content in each organ of the varieties with high cadmium accumulation was significantly higher than that of the varieties with low cadmium accumulation.A total of 11 potato HMA family genes were identified from the potato genome using bioinformatics methods,distributed on 6 chromosomes.Phylogenetic tree analysis showed that the HMA family was divided into 7 groups.Yeast heterologous expression of potato St HMA1 has cadmium transport activity,and St HMA1 was located on the potato chloroplast membrane and was highly expressed in potato leaves.St HMA3 was highly expressed in roots,and St HMA3 had allelic variation in potatoes.The St HMA3 gene(St HMA3E1)of “Eshu10” with low cadmium accumulation was 3,843 bp,and the St HMA3 gene(St HMA3H1)of “Huashu4” with high cadmium accumulation of 1281 aa was 2202 bp,encoding 734 aa,missing 4 transmembrane domains,St HMA3E1 cadmium transport activity was significantly higher than St HMA3H1 when yeast heterologous expression,this may be an important reason for the high accumulation of cadmium in “Huashu4” tubers.