Abstract:
Main conclusion Genetically engineered rice lines with
broad insecticidal properties against major lepidopteran pests were generated using a synthetic, truncated form of vegetative insecticidal protein (Syn
vip3BR) from Bacillus thuringiensis. The
selectable marker gene and the redundant transgene(s) were eliminated through Cre/lox mediated
recombination and genetic segregation to make consumer friendly Bt-rice.
For sustainable resistance against lepidopteran insect pests,
chloroplast targeted synthetic version of bioactive core
component of a vegetative insecticidal protein (Syn -
vip3BR) of Bacillus thuringiensis was expressed in rice
under the control of green-tissue specific ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit gene promoter. The transgenic plants (in Oryza sativa indica
Swarna cultivar) showed high insect mortality rate in vitro
against major rice pests, yellow stem borer (Scirpophaga
incertulas), rice leaf folder (Cnaphalocrocis medinalis) and
rice horn caterpillar (Melanitis leda ismene) in T1 generation, indicating insecticidal potency of Syn vip3BR. Under
field conditions, the T1 plants showed considerable resistance against leaf folders and stem borers. The expression
cassette (vip-lox-hpt-lox) as well as another vector with
chimeric cre recombinase gene under constitutive rice
ubiquitin1 gene promoter was designed for the elimination
of selectable marker hygromycin phosphotransferase
(hptII) gene. Crossing experiments were performed
between T1 plants with single insertion site of vip-lox-hptlox T-DNA and one T1 plant with moderate expression of
cre recombinase with linked bialaphos resistance (syn bar)
gene. Marker gene excision was achieved in hybrids with
up to 41.18 % recombination efficiency. Insect resistant
transgenic lines, devoid of selectable marker and redundant
transgene(s) (hptII ? cre-syn bar), were established in
subsequent generation through genetic segregation.
