Development of an efficient protocol for Agrobacterium mediated transformation of some recalcitrant indica rice varieties

Cloning of maize chitinase 1 gene and its expression in genetically transformed rice to confer resistance against rice blast caused by Pyricularia oryzae

Fungal pathogens are one of the major reasons for biotic stress on rice (Oryza sativa L.), causing severe productivity losses every year. Breeding for host resistance is a mainstay of rice disease management, but conventional development of commercial resistant varieties is often slow. In contrast, the development of disease resistance by targeted genome manipulation has the potential to deliver resistant varieties more rapidly. The present study reports the first cloning of a synthetic maize chitinase 1 gene and its insertion in rice cv. (Basmati 385) via Agrobacterium-mediated transformation to confer resistance to the rice blast pathogen, Pyricularia oryzae. Several factors for transformation were optimized; we found that 4-week-old calli and an infection time of 15 minutes with Agrobacterium before colonization on co-cultivation media were the best-suited conditions. Moreover, 300 μM of acetosyringone in co-cultivation media for two days was exceptional in achieving the highest callus transformation frequency. Transgenic lines were analyzed using molecular and functional techniques. Successful integration of the gene into rice lines was confirmed by polymerase chain reaction with primer sets specific to chitinase and hpt genes. Furthermore, real-time PCR analysis of transformants indicated a strong association between transgene expression and elevated levels of resistance to rice blast. Functional validation of the integrated gene was performed by a detached leaf bioassay, which validated the efficacy of chitinase-mediated resistance in all transgenic Basmati 385 plants with variable levels of enhanced resistance against the P. oryzae. We concluded that overexpression of the maize chitinase 1 gene in Basmati 385 improved resistance against the pathogen. These findings will add new options to resistant germplasm resources for disease resistance breeding. The maize chitinase 1 gene demonstrated potential for genetic improvement of rice varieties against biotic stresses in future transformation programs.