Overexpression of Glutaredoxins in Transgenic Rice to Improve High Temperature Stress Tolerance

Glutaredoxins (Grx) are small heat stable proteins. They protect cellular proteins from damage by reactive oxygen species by reducing disulfide bridges and glutathione adducts in proteins. In this study we used biotechnological tools to understand the functions of Grxs in plant tolerance to heat stress. We overexpressed (OE) Grx cDNA from fern Pteris vittata (PvGrx5) or Arabidopsis (AtGrxCp or At5G18600) as independent events in Oryza sativa cv. Nipponbare using agrobacterium-mediated transformation. Transgene expression was verified in stable T2 lines by semi-quantitative RT-PCR.  Protein extracts from GRX OE lines had significantly higher Grx activity compared to those from the vector control lines. Grx OE lines were evaluated for high temperature stress tolerance by exposing the seedlings to 37°C and 45°C at germination and V3-4 stages of plant growth respectively. The cotyledon length in PvGrx5 OE lines under heat stress were >67% of control compared to 23% in wildtype. There was no or less inhibition of shoot growth in PvGrx5 OE lines compared to higher inhibition in control lines. PvGrx5 and AtGrxCp OE lines showed signifcantly less protein oxidation following heat stress treatments. Measurement of photosynthetic efficiency showed that the PvGrx5 OE lines had significantly higher PSII efficiency under heat stressed conditions than the control lines. Together these results indicate that PvGrx5 overexpression in rice could be used to improved thermotolerance at various vegetative stages of plant growth.