Transgenic strategies for developing crops resistant to geminiviruses

Geminiviruses infect a wide range of economically important crop plants. This review covers genetic engineering approaches currently being evaluated for the development of crops resistant to geminiviruses. In the past, most of these have involved pathogen-derived resistance strategies such as the expression of mutant or truncated viral proteins that interfere with virus infection, or transcription of viral RNA sequences that silence the expression of virus genes. Recently, however, alternatives to pathogen-derived resistance have been investigated. These include the use of geminivirus-inducible toxic proteins to kill infected cells, and the expression of DNA binding proteins, peptide aptamers or GroEL homologues that either disrupt geminivirus infections or lessen their harmful effects. Despite moderate successes in the engineering of geminivirus resistance using many of these strategies, no comparative data are available either on the relative merits of different approaches, or on how well the various resistant transgenic plants that have been produced will fare in the field. We anticipate that high geminivirus mutation and recombination rates could seriously undermine the durability of most currently available resistance transgenes. It should, however, be possible to achieve robust transgenic geminivirus resistance either by using mixtures of genes targeting multiple virus processes via multiple mechanisms, or by using “tolerance” genes that alleviate symptoms but do not selectively favour resistance-breaking virus mutants.