| Gansu Province is the main potato-producing area,which is located in northern cultivation area,the planting area and output of potatoes are ranked third in China.Gansu Province is arid and semi-arid in the middle temperate zone,the development of potato industry in this region was severely restricted by the drought stress due to uneven precipitation distribution and water shortage.The combined technology of drip irrigation and film mulching has the advantages of increasing humidity and moisture,saving water and fertilizer,reducing evaporation between plants,and increasing yield and salt inhibition.In this study,the effects of different field water capacity on morphological,physiological and biochemical characteristics,tuber yield and quality,water use efficiency(WUE),and irrigation water use efficiency(IWUE)of potato plants under drip irrigation with plastic mulch were systematically studied under the rain exclusion shelter.In addition,high-throughput sequencing technology was performed to identify the differentially expression genes(DEGs)of drought sensitive and drought resistant varieties in response to drought stress,as well as the enrichment metabolic pathways and GO function analysis of DEGs.Furthermore,the Q type C2H2 transcription factor family was systematically and comprehensively analyzed to identify the candidate genes of C2H2 that were in response to drought stress.This study will provide the theoretical basis and technical support for optimizing the water-saving cultivation technology of potato in northwest China,and selecting and breeding drought-resistant potato varieties by revealing the physiological and molecular response of potato to water stress and understanding the characteristics of water demand in potato varieties.The experiments were carried out in the field under a rain exclusion shelter at the Dingxi Academy of Agricultural Science(Dingxi,Gansu Province)in 2018 and 2019.The"Hermes"potato variety was used as the material.The field experiment was carried out based on the combination of ridging and film mulching under drip irrigation to study the effects of different field water capacity(85%?95%,75%?85%,65%?75%,55%?65%,45%?55%and non-irrigation)on potato plant growth(plant height,stem diameter,branch number,main stem number,leaf number,and leaf area),dry matter accumulation and distribution,photosynthetic physiological characteristics,yield and yield components,WUE,and tuber quality.The drought-sensitive variety"Atlantic"(A)and drought-tolerant variety"Qingshu NO.9"(Q)were used as materials to perform high-throughput sequencing technology to identify the DEGs in response to drought,and analyze the metabolic pathway enrichment and functional annotation.Furthermore,the transcription factor family of Q type C2H2 in potato was systematically and comprehensively analyzed to identify the drought-responsive genes.The main results were summarized as follows:(1)With the increase of field water capacity,plant height,stem thickness,number of branches,number of leaves,leaf area and dry matter accumulation gradually increase.When the field water capacity was 75%?85%,the plant height,stem diameter,branch number,leaf number,leaf area,and dry matter accumulation of potato were the largest.When the field water capacity was 65%to 75%,the compensation effect on the number of leaves,leaf area and dry matter accumulation was significant.(2)With the increase of field water capacity,the relative water content(RWC),net photosynthetic rate(Pn),and stomatal conductance(Gs)of potato leaves were gradually increased,however,the relative chlorophyll content(SPAD)of potato leaves were gradually decreased.Compared with the non-irrigation treatment,the RWC,Pn,and Gs were significantly increased,but the SPAD was significantly reduced,with the field water capacity at 65%?75%.While the field water capacity at 75?85%,the RWC,Pn,and Gs of the potato leaves were maintained at a high level,there was not significant difference compared with the field water capacity at 85%?95%.With the increase of field water capacity,the intercellular carbon dioxide concentration(Ci)was firstly decreased,and then increased,but,the stomatal limit value(Ls)were increased firstly,and then decreased.When the field water capacity was less than 55%,Ls decreased gradually,Ci increased gradually,and Pn continued to decrease.The field water capacity at 55%?65%was the critical interval that the Pn reduction from stomatal limiting factor to non-stomatal limiting factor.(3)With the decrease of field water capacity,malondialdehyde(MDA)and proline(Pro)contents in potato leaves were gradually increased,and the activity of superoxide dismutase(SOD)were increased firstly,and then decreased.The field water capacity at 55?65%,the SOD activity of leaves was the highest,and the content of MDA and Pro was significantly higher than the treatments of the relatively high field water capacity(65%?95%).While the field water capacity was less than 55%,the SOD activity was decreased,the MDA content was continuously increased,and the leaf membrane system was irreversibly damaged.(4)Compared with the non-irrigation treatment,while the field water capacity at 65?75%,the potato tuber yield and large potato yield were significantly increased by138.82?164.69%and 19.66?19.84%,respectively.The field water capacity at 75?85%,the yield and yield of potato tuber were the best.Compared with non-irrigation treatment,the yield and yield of potato were increased by 198.99%?257.61%and24.63%?31.33%respectively.The field water capacity was more than 65%,the compensation effect on tuber large potato rate was significant.The field water capacity was more than 60%,the compensation effect on potato tuber yield was significant.(5)WUE was decreased with the increase of field water capacity,while the field water capacity at 85?95%,WUE was the lowest,about 83.84 kg·hm-2·mm-1(2018)and83.19 kg·hm-2·mm-1(2019),which was 42.61%and 54.01%,lower than non-irrigation treatment.With the increase of field water capacity,IWUE were increased firstly,and then decreased.The field water capacity was about 65%,IWUE was the highest,with82.71?86.20 kg·hm-2·mm-1.(6)The different field water capacity treatments had little effect on the contents of potato tuber dry matter,starch,reducing sugar and vitamin C.With the increase of field water capacity,the content of reducing sugar in tuber were decreased firstly,and then increased,but the content of vitamin C in tuber were increased firstly,and then decreased,with no significant difference between treatments.The tuber hardness was significantly affected by the field water holding capacity.While the field water capacity at 65%?85%,the tuber hardness was significantly higher than other treatments,and the tuber hardness was the highest with the field water capacity at 65%?75%.(7)Compared with the drought-sensitive(A)and drought-tolerant(Q)potato varieties,the number of differentially expressed genes were increased from 1620(S1)to2829(S3),with the extension of drought stress.There was a total of 4161 differentially expressed genes,which were significantly enriched in pathways of“plant hormone signal transduction”,“starch and carbohydrate metabolism”,“amino acid metabolism”,and“photosynthesis-antenna protein”.In addition,there were 194 differentially expressed transcription factors were identified,which were mainly belong to 29 transcription factor families,including b HLH,WRKY,MYB,b ZIP,NAC,C2H2,and so on.These differentially expressed genes and transcription factors may play an important role in potato response to drought stress.(8)In the whole potato genome,a total of 79 Q-type C2H2 ZFPs(St ZFP)were identified,and analyzed the physicochemical characteristics,chromosome distribution,gene structure,protein conserved domain,gene replication events,phylogenetic relationships,and expression in different tissues and abiotic stresses.According to their protein structural and phylogenetic features,these 79 St ZFPs were classified into 12 distinct subclasses.Of the 79 St ZFP genes,13 St ZFPs were specifically expressed in stolons,and two St ZFPs were specifically expressed in fruit.Eight C2H2 transcription factors,which related to potato drought resistance,were screened by RNA-seq data analysis and q PCR(Quantitative real-time-PCR)validation.Such candidate genes could provide valuable information for abiotic stress resistance research in potato. |
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