20 July 2020

Common components of the strigolactone and karrikin signaling pathways suppress root branching in Arabidopsis thaliana

Swarbreck SM, Mohammad-Sidik A, Davies JM - Plant Physiology, 2020


Elaborate root branching enables plants to efficiently access resources in a heterogeneous soil matrix. In the eudicot model species Arabidopsis (Arabidopsis thaliana), root branching occurs on the primary tap root where lateral roots (LRs) emerge to provide additional surface area for nutrient uptake and anchorage to the soil. Adventitious roots (ARs) can emerge from the root–shoot junction under normal growth conditions or from the hypocotyl under stress conditions (Steffens and Rasmussen, 2016), thus providing additional root-branching capacity. Phytohormones including strigolactones (SLs) control the development of both LRs and ARs (for review, Rasmussen et al., 2013). Higher levels of SLs, achieved through application of exogenous synthetic SL (GR24rac), tend to arrest the development of LR primordia at stage V, depending on the plant’s auxin status, and lead to overall lower LR density (LRD; Ruyter-Spira et al., 2011). GR24rac also suppresses LR priming and emergence especially near the root–shoot junction (Jiang et al., 2016). Plants insensitive to SL, such as the Arabidopsis mutant more axillary growth2 (max2) that lacks an F-box Leu-rich repeat protein (which is part of a SKP1-CULLIN-F-box class of E3 ubiquitin-ligase complex and necessary for SL perception), show an increased LRD (Kapulnik et al., 2011Ruyter-Spira et al., 2011Soundappan et al., 2015Villaécija-Aguilar et al., 2019). SLs were also shown to repress AR development (Rasmussen et al., 2012), because Arabidopsis max2 as well as mutants impaired in SL synthesis (max3 and max4) develop more ARs per plant than wild type. The max2 mutant has significantly more ARs compared to the two synthesis mutants (Rasmussen et al., 2012). Overall, the characterization of synthesis and perception mutants, as well as the use of GR24rac, has helped demonstrate a role for SL in suppressing root branching.

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