Differential Expression and Regulation of Switchgrass Root MicroRNA in Response to Alkali-salt Stress Using High-throughput Deep Sequencing

Switchgrass （Panicum virgatum L.） as a high-quality bioenergy crop that can effectively improve saline-alkali soil has strong resistance to stress and grows well in marginal soil and some abiotic stress environments.This study used alkali-sensitive genotype AM （AM-314/MS-155） and alkali-tolerant genotype ALA （Alamo） as experimental materials to investigate molecular mechanisms of switchgrass tolerance to alkali-salt stress.When the plants were grown to E5 stage,the alkali-salt stress treatment was carried out by soaking method (Na₂CO₃:NaHCO₃=1:9,C_（Na+）=150 mmol·L^-1 and pH=9.0) and fresh root samples were taken after treatments for 0 （CK）,6 and 24 h,respectively,the differentially expressed microRNAs and their regulatory network were analyzed.A total of 1 049 known miRNAs and 68 novel miRNAs were identified.Seventy-two differentially expressed miRNAs in ALA were more than three times higher than those in AM and 36.1% differentially expressed miRNAs was significantly down-regulated （p＜0.05）.Through analyses of differentially expressed miRNAs and their target genes,it was found that under alkali-salt stress,differentially expressed miRNAs in AM were mainly involved in the regulation of cellular ROS clearance,ethylene signal transduction,and root,leaf and flower development.MiRNAs in ALA were also involved in water transport,DNA methylation,response to high osmotic pressure,activation of stress-related genes and more complex responses to alkali-salt stress processes,but those in AM were not.ALA was significantly higher than AM in the number of microRNAs responding to alkali-salt stress and in the functional diversity of their regulatory target genes.