Abstract
Agrobacterium-mediated transformation of indica rice has been established in only a limited number of cultivars because the regeneration of plants from transformed embryogenic calli is highly cultivar-specific. Establishment of a highly efficient plant regeneration system from shoot apex explants applicable to many cultivars of indica rice will accelerate the application of transformation technology in breeding programs and functional genomics study. We established an efficient shoot multiplication and plant regeneration system from shoot apices of indica rice using thidiazuron (TDZ) as a plant growth regulator. Shoot apices cultured on MS basal medium devoid of plant growth regulators formed solitary shoots in 90% of cultures. Addition of TDZ or benzylaminopurine to regeneration medium significantly influenced formation of multiple shoots directly from shoot apex explants without an intervening callus stage. Best shoot proliferation response (10.3 shoots per explant) was recorded when shoot apices were cultured on media supplemented with 4 mg/l TDZ. No synergistic effect on shoot proliferation was observed when indole-3-acetic acid and indole-3-butyric acid were supplemented to media containing 4 mg/l TDZ. The regeneration system was efficient in evoking multiple shoot proliferation in eight different cultivars of indica rice. Shoots were rooted in MS basal medium and plantlets were acclimatized with 100% survival rate. The shoot apex explants of all the eight cultivars of indica rice were found competent to Agrobacterium-mediated transformation while explants from IR-64 showed highest transient GUS expression. This variety-independent transformation amenable regeneration system from shoot apices may widely be applicable for genetic transformation of indica varieties.
Highlights
Rice (Oryza sativa L.) is the main staple food for more than half of the world population
Establishment of a highly efficient plant regeneration system from shoot apex explants applicable to many cultivars of indica rice will accelerate the application of transformation technology in breeding programs and functional genomics study
We report establishment of an efficient plant regeneration system from shoot apices of indica rice applicable to eight cultivars using TDZ as a growth regulator and demonstrate their amenability to Agrobacterium-mediated transformation
Summary
Rice (Oryza sativa L.) is the main staple food for more than half of the world population. Around 80% of the world rice production is based on indica varieties, which are grown under subtropical and tropical conditions as long grain rice, and securing a unique position in agriculture (Khush 1997). It has become a model monocot system for genetic and functional genomic studies (Jung et al 2008). Considerable progress has been made in the improvement of important agronomic traits of rice through biotechnological approaches (Hao et al 2009; Skamnioti and Gurr 2009). Genetic transformation has become an important tool in targeted improvement and gene function studies in rice (Xu et al 2012). Most plant regeneration systems adapted to Agrobactrerium-mediated genetic transformation in indica rice varieties (Rashid et al 1996; Aldemita and Hodges 1996; Nayak et al 1997; Zhang et al 1997; Khanna and Raina 1999, 2002; Mohanty et al 2002; Supertana et al 2005; Ignacimuthu and Arockiasamy 2006) involve
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