Abstract
Adventitious root (AR) formation is a complex developmental process controlled by a plethora of endogenous and environmental factors. Based on fossil evidence and genomic phylogeny, AR formation might be considered the default state of plant roots, which likely evolved independently several times. The application of next-generation sequencing techniques and bioinformatics analyses to non-model plants provide novel approaches to identify genes putatively involved in AR formation in multiple species. Recent results uncovered that the regulation of shoot-borne AR formation in monocots is an adaptive response to nutrient and water deficiency that enhances topsoil foraging and improves plant performance. A hierarchy of transcription factors required for AR initiation has been identified from genetic studies, and recent results highlighted the key involvement of additional regulation through microRNAs. Here, we discuss our current understanding of AR formation in response to specific environmental stresses, such as nutrient deficiency, drought or waterlogging, aimed at providing evidence for the integration of the hormone crosstalk required for the activation of root competent cells within adult tissues from which the ARs develop.
Highlights
By definition, adventitious roots (AR) originate post-embryonically from tissues other than roots in response to different environmental signals, in a process that is highly regulated by hormonal crosstalk (Atkinson et al, 2014; Bellini et al, 2014; Steffens and Rasmussen, 2016; Gonin et al, 2019; Lakehal and Bellini, 2019)
Based on the fossil record and phylogenetic evidence, we propose Adventitious root (AR) formation as the default state of root development in plants
Recent molecular approaches using different species led to the identification of some of the conserved gene regulatory networks involved in the early steps of AR formation
Summary
Adventitious roots (AR) originate post-embryonically from tissues other than roots in response to different environmental signals, in a process that is highly regulated by hormonal crosstalk (Atkinson et al, 2014; Bellini et al, 2014; Steffens and Rasmussen, 2016; Gonin et al, 2019; Lakehal and Bellini, 2019). These results are in agreement with a conserved role of IC-WOX genes in the regulation of AR initiation in Euphyllophytes in two steps: (i) establishing the root founder cell downstream of the auxin signal and (ii) positioning the stem cell niche within the newly formed root primordia.
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