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Plant tissue culture and regeneration is implemented in many agricultural processes. It is used for the propagation of elite genotypes, to create transgenic crops, to preserve species and varieties, and to rescue or select unique genotypes for breeding.

Protocols for tissue culture and regeneration for numerous species have been developed over many decades. Most often, media composition and hormone concentrations are varied to obtain successful protocols. However, environmental factors such as light and temperature are also important. Surprisingly few studies have investigated light and temperature to improve regeneration, despite, for example, that it is well known, that darkness strongly increases adventitious rooting.

Unravelling how light inhibits adventitious rooting

(Research Foundation Flanders, FWO, 2022-2026)

The root is a highly adaptive organ providing physical support and capacity to take up and store water and nutrients. In vascular plants, the root system, with a primary root and lateral roots, mainly originates and develops from embryonic tissue. Adventitious roots on the contrary have distinct functions and emerge post-embryonically. Adventitious root formation is strongly enhanced by exogenous application of auxin, yet for many crops exposure to light inhibits rooting and a dark incubation is required for it to be successful. Despite the economic importance of root induction in cuttings, little is known about light regulation of adventitious root formation. Here we set out to discover molecular signaling components that underlay light control of adventitious root induction. With our discovery of an auxin-like compound that massively induces hypocotyl adventitious root formation in a light dependent fashion, we are encouraged to find regulators that are responsible for the suppression of rooting in the light. The results are pivotal to further our insight into the function of adventitious rooting and to develop tools that improve the rooting of shoots which is a vital component of many clonally propagated crops.

PhD project Yinwei Zeng

We identified HYSPARIN (HYS), a small molecule that induces excessive adventitious root formation on the hypocotyls of dark-grown (etiolated) seedlings that were transferred to light (Figure). HYS does not act as a bona fide auxin and is dependent on a dark light switch to induce adventitious roots. Secondly it is active when applied to the shoot part. These observations suggest that the mode of action of hysparin follows a so far undisclosed signaling pathway controlling adventitious rooting.

A) HYSPARIN (HYS) induces AR. (B) Hydrolysis of HYS may release the auxin MCPA. (C) Exposure of etiolated plants to more than 24h to white light prior to HYS prevents HYS induced AR formation.