Host Range Determinants in Plant Pathogens and Symbionts

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . ..... 421 AGROBACTERIUM TUMEFACIENS. THE CAUSAL AGENT OF CROWN GALL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . 422 Genes TJwt Broaden the Host Range . . . . .... . . . . . . .... . . . . . .... . . . . . . .. . . . . . . ... . . . . . . . .. . . . . 423 Bacterial Factors That Function Negatively to Narrow the Host Range . . . . . . . ... . . . . 424 RHIZOBIUM-LEGUME SYMBIOSIS .. .. . . .. . .. . . . .. . . . . . . .. . . . . . . ... .. . . . . . ... . . . . . ... . . . . . . . . , 424 Positive Host-Range Determinants . . . . . . .. . . . . . . . . . . ... . . . . . . . . . . . . . . . .... . . . . . ... . . . . . . . ..... 425 Negative Factors .. . .... ......... . . . .. ...... . .. . . . . . . .... 427 FACTORS DETERMINING THE HOST RANGE OF OTHER PLANT PATHOGENS 427 Pathogenicity and Virulence Factors . ... . . . . . . . . . .. . . . . . . . .. .. . .. . . . .... . . . . . . . . . . . . . . . .. . . . . 427 A virulence Genes . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . .. .. . . . . . . . . . . . . . . . . . . ... . . . . . . ... . . . . . . 429 Recent Findings From Our Own Laboratories. . . . . . ... . . . . . ....... . . . . . ... . . . . . .... . . . . . . . . 433 SUMMARY, FUTURE DIRECTIONS, AND ANTICIPATED PAYOFFS . .. . . . . . . . . .. .. 434