Lateral Root Primordium Morphogenesis in Angiosperms

Abstract

Morphogenetic processes are the basis of new organ formation. Lateral roots (LRs) are the building blocks of the root system. After LR initiation and before LR emergence, a new lateral root primordium (LRP) forms. During this period, the organization and functionality of the prospective LR is defined. Thus, proper LRP morphogenesis is a decisive process during root system formation. Most current studies on LRP morphogenesis have been performed in the model species Arabidopsis thaliana; little is known about this process in other angiosperms. To understand LRP morphogenesis from a wider perspective, we review both contemporary and earlier studies. The latter are largely forgotten, and we attempted to integrate them into present-day research. In particular, we consider in detail the participation of parent root tissue in LRP formation, cell proliferation and timing during LRP morphogenesis, and the hormonal and genetic regulation of LRP morphogenesis. Cell type identity acquisition and new stem cell establishement during LRP morphogenesis are also considered. Within each of these facets, unanswered or poorly understood questions are identified to help define future research in the field. Finally, we discuss emerging research avenues and new technologies that could be used to answer the remaining questions in studies of LRP morphogenesis.

Developmental atlas of white lupin cluster roots

“…These mechanisms may not be solely mechanical (stronger pressure, distinct cell wall remodelling processes) but may also include active cell divisions to accommodate the passage of the rootlet primordium. The existence of a temporary cap-like structure has been reported in other species (Torres-Martínez et al ., 2019) and the numerous divisions in the endodermis seem to generate such structure as can be seen on a Stage VI rootlet primordium (Fig. 1D).…”

“…As in lateral root formation of most species, divisions in the pericycle cells initiate the formation of new rootlets, but several rounds of divisions in endodermal and cortical cells are also observed. These are reminiscent of lateral root formation in other Legumes such as Medicago (Herrbach et al ., 2014) and other angiosperms (Torres-Martínez et al ., 2019). It is not entirely clear to which extent these divisions in the outer tissues contribute to the primordium itself or to a protective layer whose fate remains undescribed in white lupin.…”

At-Hook Motif Nuclear Localised Protein 18 as a Novel Modulator of Root System Architecture

“…Lateral root (LR) initiation and function of individual apical meristems significantly contribute to the establishment of root system architecture in heterogeneous soil environments, and are under precise developmental regulation. The formation of LR primordia (LRP) [1] is a complex sequential process [2,3], which in conjunction with neighboring tissues [4][5][6], starts in the parent root pericycle in seed plants. Auxin signaling was identified as a critical component of the process [7][8][9][10] alongside other phytohormones, transcription factors, and epigenetic control of the regulatory networks [11].…”

The Arabidopsis TTL3 protein interconnects brassinosteroid signalling and cytoskeleton during lateral root development

“…LR development is a complex, stepwise process (Banda et al 2019;Torres-Martinez et al 2019), regulated by a network of diverse factors. Complex biomechanical and biochemical interactions between LRP and the surrounding tissues are involved in all the steps of LRP formation -from initiation, to growth, to emergence (Vilches- Barro and Maizel, 2015;Stoeckle et al, 2018).…”