Improvement of Cold Tolerance in Rice by Cold Induced Expression of Heat Shock Genes

The world’s population will surpass 9 billion in 2050. Hence, stable food production to satisfy human demands is an important target in plant breeding programs. Cold injury is the most serious problem for stable rice production in marginal regions. However, the molecular mechanism of cold tolerance in rice is still unknown. Cold tolerance of rice seedlings can be improved by a mild cold treatment before cold treatment. Microarray analysis showed that the expression of many heat shock protein (HSP) genes increased after cold treatment. The expression of HSP genes induce tolerance to abiotic stresses such as cold, drought, or salt. Heat shock transcription factors (HSFs) play a central role in this phenomenon. We identified that the HSF gene, HsfA2c, was induced after a mild cold treatment. Our strategy was to activate HSF genes under cold conditions by using the cold-inducible promoter WCR (wheat cold response) to induce the gene expressions of HSPs under cold conditions. However, an HSP, HSP90, acted as a suppressor of HSF activity by binding to HSF, resulting in low gene expression of HSPs. To inhibit the native HSP90, we designed dominant negative HSP90 mutants (HSP90-D80N), in which the activity of HSF is not suppressed. Thus, we developed transgenic rice plants by using HsfA2c and Hsp90-D80N, which showed extremely high gene expression of HSPs under cold conditions and exhibited improved cold tolerance during various growth stages. Our results show that modification of the gene expressions of HSFs and HSPs could be useful for improving cold tolerance in rice.