Tropical areas have a large distribution of saline soils and tidal flats with a high salinity level. Salinity stress is a key factor limiting the widespread use of tropical forage such as Stylosanthes guianensis (Aubl) Sw. This study was designed to screen the salinity tolerance of 84 S. guianensis accessions; In a greenhouse experiment, plants were subjected to Hoagland solution or Hoagland solution with 200 mM NaCl for up to 15 days. Salinity tolerant accession CIAT11365 and salinity sensitive accession FM05-2 were obtained based on withered leaf rate (WLR). Further verification of salinity tolerance in CIAT11365 and FM05-2 with different salinity gradients showed that salinity stress increased WLR and decreased relative chlorophyll content (SPAD), maximum photochemical efficiency of photosystem II (Fv/Fm), and photosynthetic rate (Pn) in FM05-2, but CIAT11365 exhibited lower WLR and higher SPAD, Fv/Fm, and Pn. Leaf RNA-Seq revealed that Ca2+ signal transduction and Na+ transport ability, salinity tolerance-related transcription factors and antioxidant ability, an increase of auxin, and inhibition of cytokinin may play key roles in CIAT11365 response to salinity stress. The results of this study may contribute to our understanding of the molecular mechanism underlying the responses of S. guianensis to salinity stress and also provide important clues for further study and in-depth characterization of salinity resistance breeding candidate genes in S. guianensis.

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Highlights:1. Axonopus compressus can stand severe drought stress by activating the potential defense mechanism.2. We investigated the differential transcriptome of drought stressed and normal Axonopus compressus plants3. New comers have been identified that involved in the drought response4. Identified drought responsive genes which never known for other stresses.5. The identified genes also respond to stress in Arabidopsis thaliana in different manners.Background: Carpet grass [Axonopus compressus (L.)] is an important warm season perennial grass around the world and is renowned for its adaptability to varied environmental conditions. However, Carpet grass lacks enough data in public data bank, which confined our comprehension of the mechanism of environmental adaptations, gene discovery and development of molecular marker. Methods: In current study, the DEGs (differentially expressed genes) in Axonopus compressus under drought stress (DS) were identified and compared with CK (control) by RNA-Seq. Results: the 263,835 of total unigenes were identified in Axonopus compressus, and 201,303 (also add the numbers of remaining2 data bases) a sequence of unigenes significantly matched in at least one of the seven databases. A total of 153697 (58.25%) unigenes can be classified to 144 KEGG pathways, and 7,444 unigenes were expressed differentially between DS and CK, of which 4,249 were up-regulated and 3,195 were down-regulated unigenes. Of the 50 significantly enriched GO terms, 18, 6 and 14 items were related to BP, CC and MF, respectively. Analysis of KEGG enrichment showed 2569 DEGs involved in 143 different pathways, under drought stress 2,747 DEGs were up-regulated and 2,502 DEGs were down-regulated. Moreover, we identified 352 transcriptor factors (TFs) in Axonopus compressus, of which 270 were differentially expressed between CK and DS. The qRT-PCR validation experiment also support the transcriptional response of Axonopus compressus against drought. Conclusions: The current findings provide the first framework for further investigation for the particular roles of these unigenes in Axonopus compressus in response to droughts.