The use of grafting to study systemic signaling in plants

Grafting has long been an important technique in agriculture. Nowadays, grafting is a widely used technique also to study systemic long-distance signaling in plants. Plants respond to their surrounding environment, and at that time many aspects of their physiology are regulated systemically; these start from local input signals and are followed by the transmission of information to the rest of the plant. For example, soil nutrient conditions, light/photoperiod, and biotic and abiotic stresses affect plants heterogeneously, and plants perceive such information in specific plant tissues or organs. Such environmental cues are crucial determinants of plant growth and development, and plants drastically change their morphology and physiology to adapt to various events in their life. Hitherto, intensive studies have been conducted to understand systemic signaling in plants, and grafting techniques have permitted advances in this field. The breakthrough technique of micrografting in Arabidopsis thaliana was established in 2002 and led to the development of molecular genetic tools in this field. Thereafter, various phenomena of systemic signaling have been identified at the molecular level, including nutrient fixation, flowering, circadian clock and defense against pathogens. The significance of grafting is that it can clarify the transmission of the stimulus and molecules. At present, many micro- and macromolecules have been identified as mobile signals, which are transported through plant vascular tissues to co-ordinate their physiology and development. In this review, we introduce the various grafting techniques that have been developed, we report on the recent advances in the field of plant systemic signaling where grafting techniques have been applied and provide insights for the future.