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A strategy to make maize resistant to Striga S. Runo, B. Townsley, J. Machuka, N. Sinha RNAi (RNA interference) is the process by which production of double-stranded RNA leads to the targeted degradation of mRNA with sequence similarity and the subsequent silencing of the corresponding gene. We will use RNAi as a way to control the maize parasitic weed Striga. Striga KNOX1 (KNOTTED1-like homeobox) genes required for meristem maintenance and proper leaf patterning of organs will be targets for RNAi. A dsRNA inverted repeat construct was made by cloning 1900 bps of the polymerase chain reaction (PCR) pasted coding sequence of STM1 and KNAT1 orthologs from Striga asiatica in both sense and antisense direction and separated by 1100 bps of the rice WAXY intron under the control of 35S promoter in pMCG161. The resulting construct, pMCG161-SAKNOXi, will be transformed into maize via Agrobacterium tumefaciens. Transcription of the inserted construct will produce a hairpin structure, then a dsRNA necessary to mediate silencing of targeted STM and KNAT1 genes. It is now known that a specific mobile-silencing signal exists that can travel between cells via plasmodesmata and long distances via the phloem. Striga infects maize by sending an infectious peg (haustorium) that connects into the host’s vascular system. This physical contact between host and parasite provides a conduit for transfer of macromolecules in both directions. Evidence that gene transfer between host and parasite occurs as a result of direct physical contact between the two is provided by phylogenetic data in which plants that penetrate host plants intracellularly have been shown to pass their genes to their hosts.
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