Early-responsive molecular signatures associated with halophytic adaptation in Sesuvium portulacastrum (L.)

Sesuvium portulacastrum (L.) is a halophyte, adapted to grow naturally under high-saline environments. Under control conditions, an inverse correlation was seen between Na and K accumulation, suggesting its facultative nature and ability to use Na-K interchangeably. No significant growth reduction was seen in seedlings upto 250 mM NaCl, except for youngest leaf-curling. Significantly higher accumulation of proline (4.3/1.8-folds), glycine betaine (1.4/1.4-folds) and selected amino-acids (1.4-4.2/1.4-2.3-folds) were seen in root/shoot of seedlings within 8 h stress duration. Inspite of having higher Na-accumulation, significantly lower number of differentially expressed genes (DEGs) were identified at 24 h than 8 h stress duration, indicating transcriptional restoration. As initial hours after NaCl stress are dominated by osmotic-component, 8h-specific DEGs, which are mainly transporters and transcription factors, reflect plant's response towards NaCl-induced osmotic challenge. Most of the growth-related pathways including photosynthesis and ribosome-associated biogenesis gets suppressed, to support the activation of stress defence. Overexpression of SpRAB18 (an ABA-responsive dehydrin), one of the top-ranked DEGs, was found to impart salt-tolerance in soybean, indicating gene-function level conservation between halophyte and glycophyte. An open-access transcriptome database “SesuviumKB” (https:/ /cb.imsc.res.in/sesuviumkb) was developed to enable wide-scale gene function studies in S. portulacastrum, that could pave the way to engineer salt-tolerance in crops. Overall design: To increase our understanding of the mechanism of salinity tolerance in halophytes we investigated responses to NaCl stress in a halophyte Sesuvium portulacastrum (L.) in root and shoot tissues. We performed an experiment where NaCl stress was applied to 15 days old hydroponically grown seedlings for 8 hours and 24 hours and samples were collected prior to the stress at T0 and after the stress at T8 and T24 time points. Transcript expression profiles were generated at each of the three time points T0, T8 and T24 for samples generated from shoot and root tissues, separately. Each of the conditions had three biological replicates.