Striga hermonthica (Delile) Benth. Resistance Mechanisms in KSTP’94 Maize Variety and Host Induced Gene Silencing of CYSTEINE PROTEASE

Abstract

Striga hermonthica is a parasitic weed that causes yield losses in maize-producing countries throughout sub-Saharan Africa. A number of control methods against the noxious weed have been employed with limited success. There is therefore need to develop novel strategies for Striga control. The aim of this study was to develop technologies for using maize’s natural resistance as well as engineering RNA interference host based resistance in maize against Striga. KSTP’94 maize variety has been known to be Striga tolerant but its utilization has been limited due to scarce knowledge on the genetic mechanisms underlying this resistance. Genetic engineering through RNA interference (RNAi) offers great promise to management of parasitic plants. However, its applicability to S. hermonthica management is limited due to lack of evidence on macromolecular trafficking between host and parasite. This study sought to investigate the movement of CYSTEINE PROTEASE messenger RNA (mRNA) – a key enzyme involved in haustoria formation was used. The study first sought to determine the mechanism of host resistance to S. hermonthica through histological analysis of a tolerant (KSTP’94) and susceptible (CML 144) maize genotypes. Secondly, movement of CYSTEINE PROTEASE mRNAs from S. hermonthica to maize was investigated using semi-quantitative Reverse Transcriptase polymerase chain reaction (RT-PCR). Finally, RNAi gene construct targeting silencing of CYSTEINE PROTEASE was transformed into maize using Agrobacterium tumefaciens. Consequently, second generation transgenic maize were subjected to S. hermonthica infection assays and data on the number of S. hermonthica plants germinating as well as those attaching onto the host plants analyzed and compared with non-transformed plants. Results showed that: i) KSTP ’94 exhibited a higher level of post-attachment resistance to S. hermonthica compared to CML 144 owing to the lower number of parasite attachments, and smaller Striga seedlings with lower biomass; ii) there was trafficking of CYSTEINE PROTEASE mRNA from S. hermonthica to maize, and iii) transgenic plants expressing the CYSTEINE PROTEASE hairpin construct did not induce resistance against S. hermonthica. The resistance mechanism exhibited underscore the need to determine the genetic mechanisms underlying this resistance with the aim of integration of KSTP’94 into breeding programs.