Plant Plastid Engineering

Wani, Shabir H.; Haider, Nadia; Kumar, Hitesh; Singh, N.B.

Plastid engineering offers a new and effective option in development of plant varieties which are resistant to various bacterial and fungal diseases. In tobacco, introduction of MSI-99 gene, an antimicrobial peptide, into plastids resulted in transplastomic plants resistant to fungal pathogen Colletotrichum destructive [89] . The plastids expressed MSI-99 at high levels and showed 88% (T1) and 96% (T2) inhibition of growth against Pseudomonas syringe, which is a major plant pathogen. In another study, Agrobacterium mediated transformation was used to develop tobacco plants carrying argK gene, which encodes ROCT [90] . Since OCT in plant cells is produced in the plastid, argK was fused to the plastid transit sequence of the pea rubisco small subunit (rbcS) gene for localized expression of the enzyme. The ROCT enzyme produced by the transgenic tobacco showed greater resistance (83-100%) to phaseolotoxin compared to the wild-type OCT (0-22%). When phaseolotoxin was applied exogenously to the leaves of plants, chlorosis was observed in 100% of wildtype tobacco, but not seen in the leaves of the transgenic tobacco plants carrying the argK gene from P. syringae pv. phaseolicola. Transgenic tobacco plants that constitutively expressed both entC and pmsB in the plastid have also been reported [91] where transformation was accomplished through biolistic methods. The transgenic tobacco plants expressing these bacterial genes showed accumulation of salicylic acid that were up to 1000 times higher than that observed in wild-type tobacco. When challenged with the fungus Oidium lycopersicon, the transgenic tobacco plants showed increased levels of resistance compared to the wildtype plants. It was revealed that the transgenic plants generated did not show any adverse effects due to the high level expression of salicylic acid. Thus gene transfer in plastids can provide a significant protection from various bacterial and fungal diseases.