| Alfalfa(Medicago sativa)is the world’s most widely planted legume forage,with high nutritional value,good palatability and other characteristics,in the livestock industry has an important position.With the rapid expansion of animal husbandry,there is a strong demand for alfalfa in China,but alfalfa is very sensitive to aluminum poison in acidic soil,which seriously affects the cultivation of alfalfa in acidic soil areas in the south.Therefore,in order to improve the yield stability of alfalfa in acidic soil and understand its aluminum acid tolerance mechanism,this study used 44 alfalfa varieties as experimental materials to study the relationship between yield and yield composition factors of different varieties,and explained the trade-off between yield and yield stability from the perspective of distribution.At the same time,the transcriptome and metabolome were combined to analyze the tolerance mechanism of sensitive and tolerant alfalfa under aluminum oxide stress,which provided data support for improving the tolerance of alfalfa aluminum,in order to understand the yield stability strategy and tolerance mechanism of alfalfa in acidic soil,screen out alfalfa varieties with high yield stability,and provide basic materials and data support for the study of aluminum alfalfa acid tolerance.The main findings are as follows:(1)In different habitats,the association between alfalfa plant height and key yield-related traits such as stem thickness varies from environment to environment.The trade-off between alfalfa yield and yield stability in acidic soils of Guizhou showed that in the first year of planting,the allometric growth index was α > 1 for the varieties with the highest yield but low stability,while the varieties with the lowest yield but more stable were α < 1,and all varieties were α < 1 in the second year of planting.The results showed that in the first year of planting,the environmental resources were sufficient,and the trade-off between alfalfa yield and yield stability was mainly limited by biology and environment(such as self-stress resistance and soil p H environment).In the second year of planting,alfalfa yield and yield stability can be balanced at the right time,and alfalfa yield has high yield stability at the same time.Five high-yielding alfalfa varieties(Algonquin,Trifecta,Xinjiang Daye,WL354 HQ and Boja)were screened,and the longer the planting period in Guizhou,the better the yield and stability.(2)Under aluminum stress conditions,the content of organic acids in the roots of alfalfa cultivars differed significantly at different stress times(P < 0.05).Based on transcriptome and metabolome analysis,a total of 190,837 unigenes were assembled,of which 36,689 genes were identified as differentially expressed genes.The results of enrichment analysis showed that most of the differentially expressed genes were significantly enriched in the significant enrichment pathways such as plant pathogen interaction,starch and sucrose metabolism,and MAPK signaling pathway-plant.In addition,the analysis of differentially expressed genes WGCNA showed that citric acid and phosphoenolpyruvate played an important role in alfalfa in response to aluminum stress.Six transcription factors(b HLH,GARP-ARR-B,MYB,AP2/ERF-ERF1,AP2/ERF-ERF2 and b ZIP)that regulate citrate synthase and malate dehydrogenase were identified,which control the biosynthesis of malate and citrate by regulating the expression of specific structural genes.(3)In this study,three citrate synthase(Ms CS15,Ms CS74,Ms CS79)and two malate dehydrogenase(Ms MDH159,MSMDH190)genes were expressed heterologous in yeast and hyperexpression in AS.The results showed that the growth viability and secretion of malic acid and citric acid of transgenic yeast were significantly increased(P < 0.05)under aluminum acid stress.The citric acid secreted by transgenic alfalfa under aluminum acid stress was significantly higher(P <0.001)than that of the control. |
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