Temporal Control of Morphogenic Factor Expression Determines Efficacy in Enhancing Regeneration.

Background: Regeneration of fertile plants from tissue culture is a critical bottleneck in the application of new plant breeding technologies. Ectopic overexpression of morphogenic factors is a promising workaround for this hurdle.

Methods: Conditional overexpression of and Δ was used to study the effect of timing the overexpression of these morphogenic factors during shoot regeneration from root explants in Arabidopsis. In addition, their effect on auxin-signaling activation was examined by visualization and cytometric quantification of the DR5:GFP auxin-signaling reporter in roots and protoplasts, respectively.

Results: The induced expression of both and Δ led to an activation of auxin signaling in roots. Activation of auxin signaling by and Δ was further quantified by transient transformation of protoplasts. Ectopic overexpression of both and Δ enhanced regeneration efficiency, but only during the shoot-induction stage of regeneration and not during the callus-induction stage.

Conclusions: The overexpression of and Δ both lead to activation of auxin signaling. Expression during the shoot-induction stage is critical for the enhancement of shoot regeneration by and Δ.