Multiple Integrated Root Phenotypes Are Associated with Improved Drought Tolerance

Abstract

To test the hypothesis that multiple integrated root phenotypes would co-optimize drought tolerance, we phenotyped the root anatomy and architecture of 400 mature maize (Zea mays) genotypes under well-watered and water-stressed conditions in the field. We found substantial variation in all 23 root phenes measured. A phenotypic bulked segregant analysis revealed that bulks representing the best and worst performers in the field displayed distinct root phenotypes. In contrast to the worst bulk, the root phenotype of the best bulk under drought consisted of greater cortical aerenchyma formation, more numerous and narrower metaxylem vessels, and thicker nodal roots. Partition against medians (PAM) clustering revealed several clusters of unique root phenotypes related to plant performance under water stress. Clusters associated with improved drought tolerance consisted of phene states that likely enable greater soil exploration by reallocating internal resources to greater root construction (increased aerenchyma content, larger cortical cells, fewer cortical cell files), restrict uptake of water to conserve soil moisture (reduced hydraulic conductance, narrow metaxylem vessels), and improve penetrability of hard, dry soils (thick roots with a larger proportion of stele, and smaller distal cortical cells). We propose that the most drought tolerant integrated phenotypes merit consideration as breeding ideotypes.

The transcriptomic landscapes of diverse rice cultivars grown under mild drought conditions

“…In maize, drought-tolerant accessions have thicker roots with higher-order cortex layers and larger aerenchyma area, compared with drought-intolerant accessions, indicating that increased aerenchyma is beneficial for drought stress tolerance (Klein et al, 2020). RD_C was negatively correlated with the expression levels of ABA signaling components in root tips and leaves, suggesting that accessions with thinner roots may be more susceptible to drought conditions (Figs.…”

“…5A and 7). In maize, accessions with thicker crown roots and greater aerenchyma area perform better in drought conditions (Klein et al, 2020). Therefore, drought-stressed roots may increase aerenchyma area to adapt to drought stress with the root co-expression module M1.…”

“…Ethylene induces aerenchyma formation in the cortex, and this process depends on AUX/IAA-mediated auxin signaling (Yamauchi et al, 2020). Cortex thickness is a major determinant of root diameter (Klein et al, 2020). Hence, aerenchyma formation may be involved in reduced thickening of cortex layers, leading to thinner roots.…”

Shared genetic architecture underlying root metaxylem phenotypes under drought stress in cereals

“…Increased aerenchyma production (Zhu et al, 2010; Jaramillo et al, 2013) and larger cortical cells arranged in fewer files cheapen the root maintenance costs (Chimungu et al, 2014a; Chimungu et al, 2014b), which would allow more resources to be reallocated to deeper root construction (Lynch, 2013; Lynch et al, 2014). Additionally, many architectural and anatomical phenes are plastic, which may be an adaptive response to drought stress (Kano et al, 2011; Klein et al, 2020; Schneider et al, 2020a; Schneider and Lynch, 2020; Schneider et al, 2020b). However, less attention has been paid to root hydraulics, which have direct implications for water uptake and transport (Wasson et al, 2012; Vadez, 2014; Maurel and Nacry, 2020).…”

Deciphering the genetic basis of wheat seminal root anatomy uncovers ancestral axial conductance alleles

“…The root system architecture is responsive to spatiotemporal soil factors such as moisture and minerals availability, temperature and pH (Robbins & Dinneny, 2015). Root system characteristics including morphological and anatomical structure, carbon allocation plasticity, hydro- and gravitropism, and the rhizosheath, plays a crucial role in plants adaption and response to various environmental cues (Kitomi et al, 2020; Klein, Schneider, Perkins, Brown, & Lynch, 2020; Lynch, 2018; Rellan-Alvarez, Lobet, & Dinneny, 2016; Tracy et al, 2020; Uga et al, 2013). Better understanding of the root system genetic architecture can facilitate the development of new cultivars with ameliorate water-use efficiency for the projected climate change (Gupta, Rico-Medina, & Caño-Delgado, 2020; Palta & Turner, 2019; Preece & Peñuelas, 2020; Schneider & Lynch, 2020).…”