Molecular Cloning And Differential Expression Of SsINPS And SsP5CS Genes In Suaeda Salsa Under Salinity Stress

Upon exposure to salinity stress, plants exhibit a wide range of responses at the cellular and the whole-plant level. High concentration salinity disrupts the homeostasis in ion distribution and water potential, results in osmotic stress further and leads to the damage on various molecules, such as protein, nuleotide acid etc. It can arose growth arrest, and in some extreme condition, even death of plants. The accumulation of soluble osmolytes is a ubiquitous biochemical mechanism in bacteria, fugi, alga and almost all vascular plants adaptive to osmotic stress. Inositol and proline are two important osmopretectants which have abroad distributions and can pretect plants from the damage of osmotic stress.Previously, we have constructed a NaCl-treated cDNA library of Suaeda salsa and acquired 1000 ESTs (expressed sequence tags) by the large-scale partial sequencing of randomly selected cDNA clones, hi this research, we isolated two cDNAs that may encode a myo-inositol-1 -phosphate synthase (SsINPS, AF433879) and a delta1 -pyrroline-5-carboxylate synthase (SsPSCS, AF503911) of S. salsa We analyzed their sequence characterizations, genomic structures and transcription levels under salinity stress. The results indicated that, SsINPS showed highest homology to the INPS gene from the common ice plant (Mesembryanthemum aystallimini) and phylogenetic analysis indicated that SsINPS and McINPS share a cluster, which showed that they might be more similar in evolution. SsPSCS also showed highest homology to the according gene in M. crystallinum. Southern blot analysis showed that there is only one copy of both SsINPS and SsPSCS in the Saeda salsa genome. Northern blot analysis indicated that the expression level of SsINPS in 5". salsa leaves was significantly increased (5-10 fold) after being treated with 400mmol/L NaCl, and although the transcription level after 48 h salinity stress was lower than that of 24 h, it was still higher than the control (3-5 fold). The expression of SsPSCS increased significantly after 12 h treatment with 400mmol/L NaCl.S. salsa is euhalophyte with succulent leaves that can survive under seawater-level salinity. It had formed some specific mechanisms in salinity tolerance during the evolution. Former works investigating salt tolerance mostly focused on glycophytes. However, they arenot true halophytes, and inductions of some genes in these plants that have found to be salt responsive may only reflect salt stress damage or change in photosynthetic machinery. Finding salt-related genes in the euhalophyte S. salsa and analyzing their functions in plant responses to environmental stress may help us understand the mechanism of plant salt tolerance further, and it may also a promising strategy to plant gene engineering.