| Soil salinization has a great influence on citrus production.Studying the alkali resistance mechanism of rootstocks has important practical significance for the development of alkali-tolerant tree species and effective use of saline-alkali land.The most widely used citrus rootstock carp(Poncirus trifoliata(L.)Raf.)(abbreviated as Pt)is alkaline-sensitive,and Citrus junos Sieb.ex Tanaka(abbreviated as Cj)is alkaline-resistant.The rootstock,therefore,the purpose of this study is to analyze the molecular mechanism of the alkaline stress resistance of Ziyangxiang orange by transcriptome comparison analysis.The main findings are as follows:1.Llan Late navel orange(abbreviated as LL)was grafted on Pt and Cj respectively,and Pt+LL and Cj+LL materials were obtained and planted in calcareous soil.To efficiently and comprehensively compare the differences in transcriptome levels between Pt+LL and Cj+LL,transcriptome analysis of their roots,stems and leaves was performed using RNA-seq.In the root tissues,3431 differential genes were screened between Pt+LL and Cj+LL,and 274 and403 differential genes were screened in stem and leaf tissues,respectively.Through KEGG metabolic pathway enrichment analysis,differential genes in root tissues were significantly enriched and distributed in 20 different metabolic pathways,among which ?-linolenic acid metabolism,plant hormone signal transduction,phenylpropane biosynthesis and glutathione There are many differential genes enriched in peptide metabolism.54 differential genes were enriched in the phytohormone signal transduction pathway in the roots of Cj + LL and Pt +LL,of which 14 were enriched in the auxin signal transduction pathway and 7 were enriched in abscisic acid signaling.Of the transduction pathways,6 were enriched in the cytokinin signal transduction pathway and 5 were enriched in the jasmonic acid signal transduction pathway.In addition,the H+-transporting ATPase and Ferritin heavy chain genes were significantly different in Cj + LL_root and Pt + LL_root and Cj_root and Pt_root,suggesting that Cj is more resistant to alkali than Pt may be due to the fact that Cj can store more iron.There are 98,14,and 17 differentially expressed transcription factors in root,stem,and leaf tissues.Among these transcription factors,the number of transcription factors of the ERF family is much higher than that of other families,and most of the transcription factors of the ERF family.Up-regulation in the roots of Cj+LL suggests that the transcription factors of the ERF family may be involved in the adaptation of plants to alkaline stress.2.After 8 weeks of culture in different pH gradients,Analyzed the root morphology,mineral elements,hormones and antioxidant enzymes of the Pt and Cj(6.5,8.0,9.5).Theresults showed that under extreme alkaline conditions(pH=9.5),Pt and Cj showed significantly different phenotypes.Overall,the root structure of Pt and Cj was consistent with total root length and stem length as pH increased.The difference in total root surface area and lateral root number gradually increased.At the same time,in terms of plant phenotype and absorption of mineral elements,the number of lateral roots of Cj was much higher than Pt,and mineral nutrient absorption was better than Pt.In addition,under three pH conditions,the JA content in Cj was much higher than Pt.Under the condition of pH=8,the IAA level in Cj was significantly higher than Pt.With the increase of pH,the levels of three antioxidant enzymes: POD,SOD and CAT decreased significantly in Pt,but the magnitude of change in Cj was small.The contents of the three hormones at high pH were determined,and the contents in Pt and Cj showed significantly different differences,indicating that phytohormone may be an important regulator of citrus response to external alkali stress.3.Methyl jasmonate(MeJA)and jasmonic acid synthesis inhibitor(SHAM)applied Pt and Cj seedling experiments showed that: Under high pH conditions,it was found that the root tip growth of the 1?M MeJA clam and orange seedlings was better than that of the control group,the ROS content was lower than the control,and there was a better chlorophyll distribution and higher Fv/Fm value.The roots of the SHAM treatment group were severely necrotic,the number of LR(lateral root)was significantly reduced,the growth was not good,and the leaves had obvious yellowing.This part of the results indicates that exogenous JA inhibits the growth of LR under alkaline conditions and can remove more ROS to make the root tip of the plant healthy.4.Exogenous application of methyl jasmonate,auxin analogue and jasmonic acid synthesis inhibitor to treat Cj seedlings under high pH(Ph=8.5),it was found that exogenous application of MeJA+NAA could significantly improve the alkali resistance of Cj seedlings.The number of LR increased significantly and developed better.Indicating that the simultaneous application of auxin and jasmonic acid to Cj seedlings can promote the formation of LR,and can also eliminate ROS under alkaline stress.In short,auxin and jasmonic acid in citrus response to alkaline stress plays an important role. |
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