Identification of new circRNAs that mediate sorghum salt tolerance by attenuating ROS accumulation

As covalently closed non-coding RNAs, circular RNAs (circRNAs) play important roles in microRNA (miRNA) function regulation. To identify sorghum circRNAs and investigate functional roles they play in salt tolerance, high throughput transcriptome sequencing was performed for a salt-tolerant sorghum genotype M-81E and one salt-sensitive sorghum genotype Roma. Comparative analysis identified 87 significantly differentially expressed circRNAs (DEcircRNAs) in M-81E, of which 27 were up-regulated and 60 down-regulated. In contrast, 22 up-regulated and 62 down-regulated DEcircRNAs were identified in Roma. Competing endogenous RNA (ceRNAs) network construction identified different networks in M-81E and Roma, suggesting different circRNA-miRNA-mRNA regulatory modules in response to salt stress in the two genotypes. We then studied the functions of two circRNAs, circRNA1562 and circRNA910, from M-81E that participated in network regulation. Both transgenic plants overexpressing these two circRNAs showed increased tolerance against oxidant and ion stress caused by salt treatment. Expression patterns of these genes suggest a role of circRNA1562 in regulating the expression of SbOXS3 by competitively binding sbi-MIR399i-p5, whereas circRNA910 may be involved in regulating SbIBH1 expression by competitively binding to PC-3p-23854_516, suggesting a role of circRNAs as miRNA “sponge” by increasing target gene expression and decreasing the ROS content, so as to enhance tolerance against salt stress. Together, our work reveals the potential molecular mechanism of circRNAs in response to salt stress and provides important information for crop breeding.