Analysis On Salt Resistance Mechanism Of Fraxinus Velutina By Transcriptome,MiRNA And Degradome Sequencing

Soil salinization leads to poor growth and development of plants on them,resulting in reduced food production,threatening regional ecological security and affecting sustainable socio-economic development.Changing from managing saline land to adapt crops to selecting and breeding saline-tolerant plants to adapt to saline land,selecting salt-resistant plants and breeding salt-resistant seeds are effective ways to develop and utilize salinized soil.Fraxinus velutina Torr has a well-developed root system,is saline tolerant and highly adaptable,and is a major silvicultural species for improving inland and coastal saline lands.In this study,we identified the salt resistance characteristics of Fraxinus velutina Torr strains’R7’and’S4’by measuring chlorophyll fluorescence parameters（Fv/Fm）in their leaves and physiological indicators of roots and leaves under salt treatment,with’R7 The physiological parameters of chlorophyll fluorescence parameters（Fv/Fm）in the leaves of’R7’and’S4’as well as the physiological indexes of roots and leaves were identified,with’R7’being the salt-resistant genotype and’S4’being the salt-sensitive genotype.The transcriptome,mi RNA and degradome libraries were constructed and sequenced using Illumina sequencing platform to identify the differentially expressed genes and their regulatory pathways,and to explore the salt resistance mi RNAs and their target genes.The main findings are as follows:1.To determine the salt resistance of’R7’and’S4’:Fraxinus velutina Torr’R7’and’S4’strains were used as test materials.The chlorophyll fluorescence parameters（Fv/Fm）and physiological indicators such as proline content,soluble sugar content and H₂O₂ content in the root system and leaves were measured.The Fv/Fm values of leaves of’R7’strain were significantly higher than those of’S4’strain,and the soluble sugar and proline contents of roots of’R7’strain were significantly higher than those of’S4’strain,while the H₂O₂ contents of leaves and roots of’R7’strain were significantly higher than those of’S4’.The H₂O₂ content in the leaves and roots of’R7’was significantly lower than that of’S4’,and the physiological indexes were combined to determine the salt-tolerant genotype of’R7’and the salt-sensitive genotype of’S4’.The physiological parameters were measured to determine the salt tolerance genotype of’R7’and the salt sensitivity genotype of’S4’.2.Key genes for salt resistance in Fraxinus velutina Torr and their regulatory pathways were clarified:Transcriptome analysis of genes differentially expressed in’R7’and’S4’under250 mmol/L Na Cl stress conditions showed that in the root system of salt-resistant strain’R7’,salt stress induced up-regulation of proline biosynthesis In the root system of salt-resistant strain’R7’,salt stress induced up-regulated expression of key genes for proline biosynthesis P5CS1,and starch and sucrose biosynthesis,which enhanced the salt resistance of the root system through osmoregulation;in R7’leaves,salt stress induced the expression of phytohormone signaling genes such as PYR1/PYL/RCAR ABA receptor family genes and protein phosphorylation genes PP2C,and MAPK signaling pathway genes such as calmodulin CAM4,mitogen-activated protein kinase MPK3 and transcription factor WRKY33;enhancing the salt resistance of leaves.In addition,salt stress induced the up-regulation of 12 genes encoding POD proteins in both leaves and roots,enhancing the ROS scavenging ability of the plants.3.Salt-resistant mi RNAs and their target genes of Fraxinus velutina Torr were mined:comparative analysis of mi RNAs and degradation groups of’R7’and’S4’under 250 mmol/L Na Cl stress conditions revealed that in the salt-resistant strain’R7’root system,mi R396a,mi R156a/b,mi R8175,mi R319a/b and mi R393a targeted TGA2.3,SBP14,GR-RBP,TCP4 and TIR1 genes,respectively,to enhance salt resistance by regulating processes such as ROS scavenging and ion homeostasis;in In’R7’strain leaves,mi R164d,mi R171b/c,mi R396a and mi R160g targeted NAC1,SCL22,GRF1 and ARF18 genes,respectively,to respond to salt stress by regulating biological processes such as growth hormone signaling.In this study,we identified key genes and their regulatory pathways for salt resistance in the roots and leaves of Fraxinus velutina Torr under salt stress,and explored mi RNAs and their target genes for salt resistance in Fraxinus velutina Torr,which provide clues for a deeper understanding of the salt resistance mechanism of Fraxinus velutina Torr and contribute to the genetic improvement of salt resistance in Fraxinus velutina Torr.