Effect of NiR gene on in vitro regeneration protocol of indica, japonica, aromatic and wild rice genotypes

Efficient regeneration protocol is the prerequisite for development of transgenic plants in rice for various traits. We have found factors viz., genotype, source of explants, composition of medium and culture conditionsto be the key factors. Highest frequency of shoot regeneration was achieved when mesocotyls derived from in vitro grown seeds were cultured on MS medium supplemented with BA (0.5 mg/l). The mesocotyls produced 5 to 9 tiller shoots primarily through direct organogenesis after 3 weeks of culture. Regeneration through callusing route varied with variety. Basmati 370 only showing high percentage response to callusing, organogenesis and root formation. In between two methods studied direct shoot emergence is multiples from mesocotyls and indirect organogenesis through callusing route, the former was found efficient. The success rate being 80–100% as against 10–30% in latter. Of the genotype specificity earlier studies with temperate japonica varieties reveal regeneration efficiency to depend on the presence or absence of nitrate reductase (NiR) genes. The high response to direct organogenesis through mesocotyls when evaluated for presence or absence of NiR genes with linked markers some variation is found in band size for NiR primer amplicon. The variation could be due to deletion or insertion of a part of NiR gene across varieties. Interestingly inspite of presence of NiR genes the varietal response for callusing and organogenesis varied and correlation is not impressive enough. Thus while the study revealing no correlation between tissue culture response and presence/absence of NiR gene(s) suggests that some other genes along with NiR and its triggering factors like medium composition and type of explants are playing a combined role.