Research On The Mechanism Of Drought And Rehydration In Regulating Carbon And Nitrogen Accumulation And Distribution In Potato Tuber Swelling Stage

Potato has a wide cultivation area and accounts for a large proportion of global crops.Potato plantations are very susceptible to drought because of the low rainfall,limited water resources,shallow roots and weak ability to absorb water,so their growth is very vulnerable to water stress.The impact of the increasing global temperature and water deficit on patato production is becoming more and more serious.Therefore,it is very important to understand the physiological and molecular mechanisms of potatoes adapting to different water conditions,which is helpful to enhance the adaptability of potatoes under water stress and to cultivate drought-tolerant varieties.Pot experiments were conducted to study the response of carbon and nitrogen accumulation and transport in potato leaves and tubers to drought stress and rehydration.The expression of genes responding to different water conditions in potatoes was analyzed by transcriptome sequencing.The key genes were identified to elucidate the molecular mechanism of potato tuber expansion response to drought stress and rewatering.The important results are shown below:1.Under the dehydration,the activities of SPS in potato leaves increased,sucrose accumulated in large quantities,and the contents of sucrose and starch in tubers decreased significantly.After rehydration,the sucrose content in leaves and the sucrose and starch contents in tubers increased.It indicated that drought inhibited starch and sucrose metabolism,accumulated carbohydrates in leaves,and increased starch content in tubers after rehydration.2.Under drought stress,the activity of nitrate reductase(NR)in potato leaves decreased significantly,while the activity of glutamine synthase(GS)was not significantly different from that of control.The contents of free amino acid and soluble protein in potato leaves decreased significantly,and which of that in potato tuber increased significantly.After rewatering,the activities of NR and GS in leaves increased,the contents of free amino acids,soluble protein and total nitrogen in leaves were still lower,but higher in tubers.This indicated that drought stress promoted nitrogen distribute to tubers,and the trend was alleviated after rehydration.3.By transcriptome sequencing,19893,18886 and 19780 genes were obtained in potato leaves of control treatment,drought and rewatering,respectively.After dehydration,3530 genes were identified,of which 1393 were up-regulated and 2137 were down-regulated.In the leaves,3308 genes were up-regulated,including 1980 up-regulated and 1328down-regulated,respectively.There were 17855,17186 and 17544 genes in potato tubers under control,dehydration and rehydration,respectively.In tubers,there were 1357 genes after dehydration,of which 729 were up-regulated and 628 were down-regulated.The number of genes between rehydration and dehydration was 4663,of which 2619 were up-regulated and 2044 were down-regulated.Twenty-seven were identified by q RT-PCR,which indicated that the transcriptome data were reliable.4.The results of KEGG annotation showed that the genes in leaves were mainly related to glycosyltransferase,ribosomal protein,serine/threonine protein kinase and receptor protein,and in tubers were mainly related to peroxidase,oxidase and transcription factors.In leaves,1372 genes were annotated in 118 KEGG metabolic pathways under dehydration,and 1781 genes were enriched in 118 metabolic pathways after rehydration.The metabolic pathways of genes under dehydration included secondary metabolic biosynthesis pathway,plant hormone signal transduction pathway and starch and sucrose metabolic pathway.The pathways include plant hormone signal transduction,biosynthetic pathway of secondary metabolites,carbon metabolism pathway and glycolysis/gluconeogenesis pathway.In tubers,661 genes were annotated in 100 KEGG metabolic pathways under dehydration,and 2563 genes were annotated in 121 KEGG metabolic pathways after rehydration.The metabolic pathways of genes enriched pathways under dehydration were mainly plant hormone signal transduction pathway,protein processing in endoplasmic reticulum,phenylalanine metabolic pathway,etc.Carbon metabolism,amino acid biosynthesis,pyruvate metabolism and other pathways after rehydration.5.Under drought stress,the expression levels of SPS and Su Sy genes in leaves were positively correlated with the activities of SPS and SS,which promoted the accumulation of sucrose and decreased the sucrose content in tubers.The down-regulation of SPS and Su Sy genes in leaves after rehydration indicated that the molecular level had initiated the regulation mechanism of reducing sucrose content in leaves and the accumulation of sucrose in tubers.Under drought stress,the expression level of tuber SBE gene was positively correlated with starch content,and starch accumulation was inhibited.After rehydration,tuber SBE and AGP were positively correlated with starch content,promoting starch synthesis and accumulation.The combination of molecular and physiological levels indicates that water stress hinders the distribution of carbohydrates into the tubers and recovers after rehydration.