The cap size and shape of Arabidopsis thaliana primary roots impact the root responses to an increase in medium strength

Abstract

During root progression in soil, root cap cells are the first to encounter obstacles. The root cap is known to sense environmental cues, making it a relevant candidate for a mechanosensing site. An original two-layer medium was developed in order to study root responses to growth medium strength and the importance of the root cap in the establishment of these responses. Root growth and trajectory of primary roots of Arabidopsis thaliana seedlings were investigated using in vivo image analysis. After contact with the harder layer, the root either penetrated it or underwent rapid curvature, enabling reorientation of the root primary growth. The role of the root cap in tip reorientation was investigated by analyzing the responses of Arabidopsis mutant roots with altered caps. The primary root of fez-2 mutant lines, which has fewer root cap cell layers than wild-type roots, showed impaired penetration ability. Conversely, smb-3 roots of mutant lines, which display a higher number of root cap cells, showed enhanced penetration abilities. This work highlights that alterations in root cap shape and size affect the root responses to medium strength.HighlightThe analysis of the growth and orientation of Arabidopsis thaliana mutant roots affected in root cap size and shape showed that properly formed root cap is required to trigger the root responses to medium strength.AbbreviationsCOLcolumella;LRCLateral Root Cap;SISharpness Index;SMBSOMBRERO.

ROOT PENETRATION INDEX 3, a major quantitative trait locus associated with root system penetrability in Arabidopsis

“…In this context, it has been suggested that touchdependent gravitropic and thigmotropic responses, which include sundry root growth patterns such as root tortuosity/circumnutation function (Taylor et al, 2021), buckling (Silverberg et al, 2012), skewing (Roy and Bassham, 2017), coiling/curling (Lourenco et al, 2015) and waving (Tan et al, 2015), could facilitate root penetration into hard surfaces. At anatomical and morphological levels, a plethora of root specific traits have been reported to be associated with root penetrability such as cortical thickness, stele diameter (Chimungu et al, 2015), root hair density (Bengough et al, 2016), mucilage production (Iijima et al, 2004), sloughing of root cap cells (Bengough and McKenzie, 1997) and root tip geometry (Colombi et al, 2017;Roué et al, 2020). In maize (Zea mays) and wheat (Triticum aestivum), root genotypes with multiseriate cortical sclerenchyma showed greater lignin concentration and bending strength, which in turn, improve their penetration ability in compacted soils (Schneider et al, 2021).…”