Overexpression of Arabidopsis <i>ICE1</i> enhances yield and multiple abiotic stress tolerance in indica rice

Abstract

ICE1 (Inducer of CBF Expression 1), a MYC-type bHLH transcription factor, is a regulator of cold tolerance in Arabidopsis. Indica rice, which occupies the major rice cultivated area, is highly sensitive to cold stress. Hence in this study, Arabidopsis <i>ICE1</i> (<i>AtICE1</i>) was overexpressed in indica rice to analyze its role in reproductive stage cold and other abiotic stress tolerance to indica rice. <i>AtICE1</i> was overexpressed by using stress inducible <i>AtRD29A</i> promoter in mega rice cv. MTU1010. Under cold stress conditions, <i>AtICE1</i> overexpression lines showed lower accumulation of MDA and H₂O₂, higher membrane stability, and thus higher seedling survival rate than the WT plants. Expression levels of <i>OsDREB1A, OsMYB3R2</i>, and <i>OsTPP1</i> were significantly higher in transgenics as compared with WT under cold stress conditions. <i>AtICE1</i> transgenic rice plants produced 44-60% higher grain yield as compared with WT plants under control conditions in three independent experiments. Of the three <i>AtICE1</i> overexpression lines, two lines produced significantly higher grain yield as compared with WT plants after recovery from cold, salt and drought stresses. <i>AtICE1</i> overexpression lines showed significantly higher stomatal density and conductance under non-stress conditions. qRT-PCR analysis showed that expression levels of stomatal pathway genes viz., <i>OsSPCH1, OsSPCH2, OsSCR1, OsSCRM1, OsSCRM2</i> and <i>OsMUTE</i> were significantly higher in <i>AtICE1</i> transgenics as compared with WT plants. The components of water use viz., stomatal conductance, photosynthesis, and instantaneous WUE were higher in transgenics as compared with WT plants. The results showed that <i>AtICE1</i> confers multiple stress tolerance to indica rice, and the role of <i>ICE1</i> in stress tolerance and stomatal development is conserved across species.