Molecular Cloning and Functional Analysis of Salt Overly Sensitive (SOS) Pathway Genes from Local Plants of the United Arab Emirates

Salinity is one of the major abiotic stresses that lead to extreme reduction in crop productivity worldwide. Increased soil and water salinity is a major issue in UAE’s agriculture. Some plants however have adapted to grow in high saline conditions, i.e. halophytes. Unfortunately, most crops are glycophytes and cannot tolerate high salinity. During salinity stress, expression of numerous genes is altered to protect the plants. Understanding the differences in gene structure between halophytes and glycophytes could provide insights into developing transgenic crops that can thrive in salinity conditions. The Salt Overly Sensitive (SOS) pathway is a key mechanistic cascade controlling cellular ion homeostasis during salinity stress. In this study, the SOS pathway genes (SOS1, SOS2, SOS3) have been isolated from Avicenna marina, (a mangrove adapted to the coastal regions of UAE), Prosopis cineraria (a desert adapted plant species), and Panicum turgidum (a halophytic grass). The SOS genes from these plants were cloned by reverse-transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). The full-length ORFs of AmSOS1, PcSOS1 and PtSOS1 are 3426 bp, 3456 bp, and 3453 bp respectively. The putative AmSOS1, PcSOS1, and PtSOS1 proteins all have 12 transmembrane domains plus a cyclic nucleotide binding domain (CNBD), an auto-inhibitory domain and the SOS2 binding domain. AmSOS1 also contains an N-terminal signal peptide. Overall, the amino acid sequences of these proteins are similar to AtSOS1 with most of the variations being in the auto-inhibitory domain. Furthermore, the full-length ORFs of AmSOS2 and PtSOS2 are 1341 bp and 1374 bp respectively. AmSOS2 and PtSOS2 both contain the kinase domain in the N-terminals followed by the FISL motif and the Protein Phosphatase Interaction (PPI) motif in the regulatory domain. PPI motif has the most variations when compared to AtSOS2. Moreover, the full length ORF of PtSOS3 is 636 bp and the partial ORF of AmSOS3 is 540 bp. The putative PtSOS3 and AmSOS3 contain four EF-hands that are similar to that of AtSOS3. However, there are some variations in the Ca+ binding residues. In this study, to investigate the function of the SOS1 gene isolated from Avicenna marina, sos1-1 mutant and wild type Arabidopsis thaliana were transformed with wild type AmSOS1 and its constitutive form Am SOS1Δ946. The preliminary analysis of transgenic T2 lines derived from the sos1-1 mutant transformed with AmSOS1 rescued the salt sensitive phenotype of the mutants. This shows that AmSOS1 is expressed in the transgenic Arabidopsis thaliana and functions similarly to AtSOS1. Hence, indicates that the isolated AmSOS1 is indeed an ortholog of At SOS1. In addition, both AmSOS1 and the constitutive form AmSOS1Δ946 were able to increase the salt tolerance in wild type Arabidopsis thaliana. However, AmSOS1Δ946 displayed stronger effect than the wild type AmSOS1 suggesting AmSOS1Δ946 is more active. Although further in depth functional analysis is needed, the present study opens the use of the SOS pathway genes isolated from local salt tolerant plants to transform crop plants of interest to enhance salinity tolerance