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Summary Brace roots are a unique but poorly understood set of organs found in some large cereal crops such as maize. These roots develop from aerial stem nodes and can remain aerial or grow into the ground. Despite their name, the function of these roots to brace the plant was only recently shown. In this article, I discuss the current understanding of brace root function and development, as well as the multitude of open questions that remain about these fascinating organs. 

Root lodging, the agronomic term for plant mechanical failure, causes yield loss in crops, including maize. Brace roots can provide structural support and assist in preventing root lodging. While the mechanics of brace roots (e.g., stiffness and strength) can play a role in their ability to prevent root lodging, there has been limited characterization of individual brace root mechanical properties. Methods to quantify root mechanics can thus be useful for characterizing maize mechanical traits and breeding new varieties with improved root anchorage and lodging resistance. Here, we describe a protocol for evaluating mechanical properties of maize brace roots. Specifically, we outline the steps necessary to perform three-point bend mechanical testing of maize brace roots using an Instron Universal Testing Stand. We describe root preparation, instrument setup, method establishment, testing, and data analysis. While we exemplify the protocol using maize brace roots, the approach can be adapted for assessing the mechanics of other plants or root types. 

The mechanical properties of individual roots and entire root systems play key roles in essential root functions such as water and nutrient acquisition, defense against soil microorganisms, and plant anchorage. However, relatively few studies have quantified the mechanics (e.g., stiffness and strength) of individual and entire root systems, or explored the link between root mechanics and root functions. This limitation is likely due to a lack of standardized methods for quantifying root mechanical properties, and has created a gap in our understanding of how root mechanical traits contribute to root functions. To date, most of our knowledge comes from studies in maize, where mechanical failure (i.e., root lodging) has detrimental impacts on crop yield. Here, we review the importance of root mechanics for maize production and discuss methods used to measure individual and entire root system mechanics. 

Plants have a remarkable ability to generate organs with a different identity to the parent organ, called ‘trans-organogenesis’. An example of trans-organogenesis is the formation of roots from stems (a type of adventitious root), which is the first type of root that arose during plant evolution. Despite being ancestral, stem-borne roots are often contextualised through lateral root research, implying that lateral roots precede adventitious roots. In this review we challenge that idea, highlight what is known about stem-borne root development across the plant kingdom, the remarkable diversity in form and function, and the many remaining evolutionary questions. Exploring stem-borne root evolutionary development can enhance our understanding of developmental decision making and the processes by which cells acquire their fates. 

Brace roots (roots developing from aerial stem nodes) are a type of adventitious root that develop from aboveground stem nodes in many monocots. Brace roots may remain aerial or penetrate the soil as they perform root functions such as anchorage and resource acquisition. Although brace root development in soil or aerial environments influences function, a lot is still unknown about how their anatomy, architecture and development contributes to their function. This article summarizes the current state of knowledge on brace roots.