Analysis of N6-methyladenosine reveals a new important mechanism regulating the salt tolerance of sweet sorghum

The N6-methyladenosine (m6A) modification is the most common internal post-transcriptional modification, with important regulatory effects on RNA export, splicing, stability, and translation. Studies on the m6A modifications in plants have focused on Arabidopsis thaliana growth and development. However, A. thaliana is a salt-sensitive and model plant species. Thus, studies aimed at characterizing the role of the m6A modification in the salt stress responses of highly salt-tolerant crop species are needed. Sweet sorghum is cultivated as an energy and forage crop, which is highly suitable for growth on saline-alkaline land. Exploring the m6A modification in sweet sorghum may be important for elucidating the salt-resistance mechanism of crops. In this study, we mapped the m6A modifications in two sorghum genotypes (salt-tolerant M-81E and salt-sensitive Roma) that differ regarding salt tolerance. The m6A modification in sweet sorghum under salt stress was drastically altered, especially in Roma, where the m6A modification on mRNAs of some salt-resistant related transcripts increased, resulting in enhanced mRNA stability, which in turn was involved in the regulation of salt tolerance in sweet sorghum. Although m6A modifications are important for regulating sweet sorghum salt tolerance, the regulatory activity is limited by the initial m6A modification level. Additionally, in M-81E and Roma, the differences in the m6A modifications were much greater than the differences in gene expression levels and are more sensitive. Our study suggests that the number and extent of m6A modifications on the transcripts of salt-resistance genes may be important factors for determining and assessing the salt tolerance of crops.