OsRuvBL1a DNA helicase boost salinity and drought tolerance in transgenic indica rice raised by in planta transformation

RuvBL, is a member of SF6 superfamily of helicases and is conserved among the various model systems. Recently, rice (Oryza sativa L.) homolog of RuvBL has been biochemically characterized for its ATPase and DNA helicase activities; however its involvement in stress has not been studied so far. Present investigation reports the detailed functional characterization of OsRuvBL under abiotic stresses through genetic engineering. An efficient Agrobacterium-mediated in planta transformation protocol was developed in indica rice to generate the transgenic lines and study was focused on optimization of factors to achieve maximum transformation efficiency. Overexpressing OsRuvBL1a transgenic lines showed enhanced tolerance under in vivo salinity stress as compared to WT plants. The physiological and biochemical analysis of the OsRuvBL1a transgenic lines showed better performance under salinity and drought stresses. Several stress responsive interacting partners of OsRuvBL1a were identified using Y2H system revealed to its role in stress tolerance. Functional mechanism for boosting stress tolerance by OsRuvBL1a has been proposed in this study. This integration of OsRuvBL1a gene in rice genome using in planta transformation method helped to achieve the abiotic stress resilient smart crop. This study is the first direct evidence to show the novel function of RuvBL in boosting abiotic stress tolerance in plants.

Marker-free transgenic rice plant overexpressing pea LecRLK imparts salinity tolerance by inhibiting sodium accumulation

KEY MESSAGE

PsLecRLK overexpression in rice provides tolerance against salinity stress and cause upregulation of SOS1 pathway genes, which are responsible for extrusion of excess Na+ ion under stress condition. Soil salinity is one of the most devastating factors threatening cultivable land. Rice is a major staple crop and immensely affected by soil salinity. The small genome size of rice relative to wheat and barley, together with its salt sensitivity, makes it an ideal candidate for studies on salt stress response caused by a particular gene. Under stress conditions crosstalk between organelles and cell to cell response is imperative. LecRLK is an important family, which plays a key role under stress conditions and regulates the physiology of the plant. Here we have functionally validated the PsLecRLK gene in rice for salinity stress tolerance and hypothesized the model for its working. Salt stress sensitive rice variety IR64 was used for developing marker-free transgenic with modified binary vector pCAMBIA1300 overexpressing PsLecRLK gene. Comparison of transgenic and wild-type (WT) plants showed better physiological and biochemical results in transgenic lines with a low level of ROS, MDA and ion accumulation and a higher level of proline, relative water content, root/shoot ration, enzymatic activities of ROS scavengers and upregulation of stress-responsive genes. Based on the relative expression of stress-responsive genes and ionic content, the working model highlights the role of PsLecRLK in the extrusion of Na+ ion from the cell. This extrusion of Na+ ion is facilitated by higher expression of SOS1 (Na+/K+ channel) in transgenic plants as compared to WT plants. Altered expression of stress-responsive genes and change in biochemical and physiological properties of the cell suggests an extensive reprogramming of the stress-responsive metabolic pathways by PsLecRLK under stress condition, which could be responsible for the salt tolerance capability.

Stress-induced Oryza sativa RuvBL1a is DNA-independent ATPase and unwinds DNA duplex in 3' to 5' direction

RuvB, a member of AAA+ (ATPases Associated with diverse cellular Activities) superfamily of proteins, is essential, highly conserved and multifunctional in nature as it is involved in DNA damage repair, mitotic assembly, switching of histone variants and assembly of telomerase core complex. RuvB family is widely studied in various systems such as Escherichia coli, yeast, human, Drosophila, Plasmodium falciparum and mouse, but not well studied in plants. We have studied the transcript level of rice homologue of RuvB gene (OsRuvBL1a) under various abiotic stress conditions, and the results suggest that it is upregulated under salinity, cold and heat stress. Therefore, the OsRuvBL1a protein was characterized using in silico and biochemical approaches. In silico study confirmed the presence of all the four characteristic motifs of AAA+ superfamily-Walker A, Walker B, Sensor I and Sensor II. Structurally, OsRuvBL1a is similar to RuvB1 from Chaetomium thermophilum. The purified recombinant OsRuvBL1a protein shows unique DNA-independent ATPase activity. Using site-directed mutagenesis, the importance of two conserved motifs (Walker B and Sensor I) in ATPase activity has been also reported with mutants D302N and N332H. The OsRuvBL1a protein unwinds the duplex DNA in the 3' to 5' direction. The presence of unique DNA-independent ATPase and DNA unwinding activities of OsRuvBL1a protein and upregulation of its transcript under abiotic stress conditions suggest its involvement in multiple cellular pathways. The first detailed characterization of plant RuvBL1a in this study may provide important contribution in exploiting the role of RuvB for developing the stress tolerant plants of agricultural importance.