Direct conversion of root primordium into shoot meristem relies on timing of stem cell niche development

Abstract

To understand how the identity of an organ can be switched, we studied the transformation of lateral root primordia (LRP) into shoot meristems in Arabidopsis root segments. In this system, the cytokinininduced conversion does not involve the formation of callus-like structures. Detailed analysis showed that the conversion sequence starts with a mitotic pause and is concomitant with the differential expression of regulators of root and shoot development. The conversion requires the presence of apical stem cells, and only LRP at stages VI or VII can be switched. It is engaged as soon as cell divisions resume because their position and orientation differ in the converting organ compared with the undisturbed emerging LRP. By alternating auxin and cytokinin treatments, we showed that the root and shoot organogenetic programs are remarkably plastic, as the status of the same plant stem cell niche can be reversed repeatedly within a set developmental window. Thus, the networks at play in the meristem of a root can morph in the span of a couple of cell division cycles into those of a shoot, and back, through transdifferentiation.

Plant stem cells and de novo organogenesis

“…Likewise, the wox5 wox7 mutant led to defects in patterning of root stem cell niche and reduced root regeneration, whereas overexpressing WOX5 increased the number of regenerated root (Hu & Xu, ). It has been shown recently that shoot converted from root primordium by exogenous cytokinin can be reverted into lateral root by auxin (Rosspopoff et al ., ). The expression of WUS or WOX5 is induced before organ conversion.…”

Mechanisms of vegetative propagation in bulbs : a molecular approach

“…Upon SIM culture, Shoot regeneration from Arabidopsis root explants is also possible upon direct culture on cytokinin-rich SIM (Atta et al 2009;Chatfield et al 2013;Rosspopoff et al 2017). In this system the pre-existing lateral root primordia (LRP) along the pericycle layer in the root undergo fate re-determination into shoot apical meristems (SAMs) (Atta et al 2009).…”

“…In this system the pre-existing lateral root primordia (LRP) along the pericycle layer in the root undergo fate re-determination into shoot apical meristems (SAMs) (Atta et al 2009). Once the root is transferred to SIM, the auxin maxima normally building up in the pre-existing LRP disappear together with the expression of root marker genes, such as PLETORA1 (PLT1) and SHORT ROOT (SHR) (Rosspopoff et al 2017). At the same time, the mitotic activity of the LRP is halted.…”

“…Once cell division resumes, de novo auxin biosynthesis, PIN1 re-localization and STM and WUS expression take place at the top half of the primordium. As the pro-meristem is formed, the domain of expression of shoot genes resembles the spatial organization of expression in a SAM (Rosspopoff et al 2017). …”

DNA METHYLTRANSFERASE1‐mediated shoot regeneration is regulated by cytokinin‐induced cell cycle in Arabidopsis

“…Shoot regeneration includes callus formation and shoot induction. The callus is induced by a genetic pathway of lateral root initiation or by wounding (Atta et al, 2009;Sugimoto et al, 2010;Iwase et al, 2011;Rosspopoff et al, 2017). Many studies have uncovered key factors controlling callus formation, including WUSCHEL RELATED HOMEOBOX11 (WOX11) and WOX12 (Liu et al, 2014), PLETHORA (PLT) (Kareem et al, 2015), LATERAL ORGAN BOUNDARIES DOMAIN (LBD) (Fan et al, 2010), WOUND INDUCED DEDIFFERENTIATION 1 (WIND1) (Iwase et al, 2011) and ENHANCER OF SHOOT REGENERATION1 (ESR1) (Iwase et al, 2017).…”