Improvement of Bacterial Blight Resistance in Two Conventionally Cultivated Rice Varieties by Editing the Noncoding Region

Abstract

<i>xa13</i> is a recessive pleiotropic gene that positively regulates rice disease resistance and negatively regulates rice fertility; thus, seriously restricting its rice breeding application. In this study, CRISPR/Cas9 gene-editing technology was used to delete the <i>Xa13</i> gene promoter partial sequence, including the pathogenic bacteria-inducible expression element. Rice with the edited promoter region lost the ability for pathogen-induced gene expression without affecting background gene expression in leaves and anthers, resulting in disease resistance and normal yield. The study also screened a family of disease-resistant and normal fertile plants in which the target sequence was deleted and the exogenous transgene fragment isolated in the T₁ generation (transgene-free line). Important agronomic traits of the T₂ generation rice were examined. T₂ generation rice with/without exogenous DNA showed no statistical differences compared to the wild type in heading stage, plant height, panicles per plant, panicle length, or seed setting rate in the field. Two important conventional rice varieties, namely Kongyu131 (KY131, <b><i>Geng</i></b>/<i>japonica</i>) and Huanghuazhan (HHZ, <b><i>Xian</i></b>/<i>indica</i>), were successfully transformed, and disease-resistant and fertile materials were obtained. Currently, these are the two important conventional rice varieties in China that can be used directly for production after improvement. Expression of the <i>Xa13</i> gene in the leaves of transgenic rice (KY-PD and HHZ-PD) was not induced after pathogen infection, indicating that this method can be used universally and effectively to promote the practical application of <i>xa13</i>, a recessive disease-resistant pleiotropic gene, for rice bacterial blight resistance. Our study on the regulation of gene expression by editing noncoding regions of the genes provides a new idea for the development of molecular design breeding in the future.