Cell wall properties play an important role in the emergence of lateral root primordia from the parent root

Peter S Roycewicz,Jocelyn E Malamy

doi:10.1093/jxb/eru056

Abstract

Plants adapt to their unique soil environments by altering the number and placement of lateral roots post-embryonic. Mutants were identified in Arabidopsis thaliana that exhibit increased lateral root formation. Eight mutants were characterized in detail and were found to have increased lateral root formation due to at least three distinct mechanisms. The causal mutation in one of these mutants was found in the XEG113 gene, recently shown to be involved in plant cell wall biosynthesis. Lateral root primordia initiation is unaltered in this mutant. In contrast, synchronization of lateral root initiation demonstrated that mutation of XEG113 increases the rate at which lateral root primordia develop and emerge to form lateral roots. The effect of the XEG113 mutation was specific to the root system and had no apparent effect on shoot growth. Screening of 17 additional cell wall mutants, altering a myriad of cell wall components, revealed that many (but not all) types of cell wall defects promote lateral root formation. These results suggest that proper cell wall biosynthesis is necessary to constrain lateral root primordia emergence. While previous reports have shown that lateral root emergence is accompanied by active remodelling of cell walls overlying the primordia, this study is the first to demonstrate that alteration of the cell wall is sufficient to promote lateral root formation. Therefore, inherent cell wall properties may play a previously unappreciated role in regulation of root system architecture.

Highlights

Post-embryonic development is the plant’s means of coping with immobility
It is useful to have a pipeline to categorize mutants into subgroups representing known mechanisms for increased lateral root formation. Such a pipeline is described here for a group of eight mutants that were isolated with increased lateral root formation, and which were rescreened for lateral root emergence mutants of interest
Seedlings grown under these repressive conditions have been previously reported to show a dramatic decrease in lateral root formation compared with seedlings grown under control conditions (control conditions were defined as 1× MS basal salts, 5 mM each KNO3 and NH4NO3 and 1% sucrose, and low light (50–60 μmol) (Macgregor et al, 2008)

Summary

Introduction

Post-embryonic development is the plant’s means of coping with immobility. It gives plants a way to adapt to the chaotic nature of the world around them. It allows plants to ‘move’, slowly and methodically, towards that which they need most in life: sunlight, nutrients, and water. The latter two elements reside beneath the soil. Those belonging to the clade eudicotyledon (including the model plant Arabidopsis thaliana), the complex adult root system originates from a single embryonic root. From this root develop new autonomous lateral roots. These roots give rise to more roots, and so the pattern continues. This process is neither fixed nor random, but rather highly dependent on the environment that surrounds it (Malamy, 2005, 2009; Jung and McCouch, 2013)

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Conclusion