Full-length transcriptome analysis of asparagus roots reveals the molecular mechanism of salt tolerance induced by arbuscular mycorrhizal fungi

Abstract

Soil salinity is one of the most serious abiotic stresses that limit agricultural productivity and the distribution of crops worldwide. Arbuscular mycorrhizal fungi (AMF) can improve the salt tolerance of host plants. A systematic study on plant responses to AMF under salinity stress may provide insights into the acquired salt tolerance. Here, we performed transcriptome sequencing using the Oxford Nanopore Technologies (ONT) MinION platform for asparagus (Asparagus officinalis L.) roots with 4 treatments: non-inoculated plants under optimal growth conditions (NI), inoculated plants under optimal growth conditions (AMF), non-inoculated plants under salinity stress conditions (NI + S), and inoculated plants under salinity stress conditions (AMF + S). A total of 6124 differentially expressed transcripts (DETs) were determined. Based on Venn diagram analysis, 391 DETs were specially regulated by AMF under salinity stress rather than under optimal growth conditions, which may be linked to the salinity stress adaptation mediated by AMF. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses revealed that these transcripts mainly involved the regulation of ROS-scavenging capacity, water and nutrient status, and cell wall synthesis and modification. Furthermore, 23 differentially expressed transcription factors (TFs) were identified in the NI + S and AMF + S comparison, which are known to be associated with plant abiotic and biotic stress responses and regulation. Moreover, the identification of alternative splicing (AS) events indicated a more comprehensive response to AMF at the post-transcriptional level, which mainly occurs in genes involved in cell wall-related processes, transport, regulation of transcription, and response to abiotic stimulus. These results provide important insights into the salt tolerance induced by AMF and a solid basis for the future enhancement of plant tolerance to salinity stress.