Transcriptome analysis reveals the main metabolic pathway of c-GMP induced by salt stress in tomato seedlings

Tomato is a model crop, as well as important food worldwide. In the arid areas, aggravation of soil salinity has become the primary problem that threatens the high yield in tomato production. As a second messenger substance, cyclic guanosine monophosphate (c-GMP) plays an indispensable role in plant response to salt stress through regulating cell processes to promote plant growth and development. However, this mechanism has not been fully explored in tomato seedlings. In this experiment, the tomato seeds were cultured in distilled water (CK), 20 M c-GMP (T1), 50 mM NaCl (T2), 20 M c-GMP + 50 mM NaCl (T3). The results show that 20 M c-GMP effectively alleviated the inhibition of 50 mM NaCl on tomato growth and development, inducing the expression of 1580 DEGs. 95 DEGs were up-regulated and 442 DEGs were down-regulated (CK vs T1), whereas in the T2 vs T3 comparison 271 DEGs were up-regulated and 772 DEGs were down-regulated. Based on KEGG analysis, the majority of DEGs were involved in metabolism; exogenous c-GMP induced significant enrichment of pathways associated with carbohydrates, phenylpropanoids and fatty acid metabolism. Most PMEs, acCoA, PAL, PODs, FADs, and AD were up-regulated, and GAPDHs, PL, PG, BXL4, and {beta}-G were down-regulated, which reduced susceptibility of tomato seedlings to salt and promoted their salt adaptation. The application of c-GMP promoted soluble sugar, flavonoids and lignin content, reduced accumulation of MDA, and enhanced the activity of POD. Thus, our results provide insights into the molecular mechanisms associated with salt tolerance of tomato seedlings.