Plant Genetic Control of Nodulation

INTRODUCTION 345 LEGUME NODULATION . . ........ ....... ... .. ... . . ....... ..... ........ . 346 ROLE OF THE BACTERIAL SYMBIONT: SIGNAL EXCHANGE 348 NODULATION AS A DEVELOPMENTALLY REGULATED PHENOMENON....... 354 PLANT NODULATION MUTANTS 357 NODULATION CONTROL IN LEGUMES 361 AUTOREGULATION ...... ........ 362 What Is the Signal Transduction Mechanism? an Example of Systemic Root-Shoot Interaction .... .. . .. .... .. ....... '''''''''''''''''''''''''' .. .. ,, 363 How Is Nodulation Suppressed? 364 What Triggers the Systemic Response?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365 A Working Hypothesis. . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . ..... . . . . . . . . . . . . . ... .. . 367 NODULATION IN THE ABSENCE OF RHIZOBIUM SPP. 368 PERSPECTIVES 370