Genetic control of root anatomical plasticity in maize

Abstract

Root anatomical phenes have important roles in soil resource capture and plant performance; however, their phenotypic plasticity and genetic architecture is poorly understood. We hypothesized that (a) the responses of root anatomical phenes to water deficit (stress plasticity) and different environmental conditions (environmental plasticity) are genetically controlled and (b) stress and environmental plasticity are associated with different genetic loci than those controlling the expression of phenes under water‐stress and well‐watered conditions. Root anatomy was phenotyped in a large maize (Zea mays L.) association panel in the field with and without water deficit stress in Arizona and without water deficit stress in South Africa. Anatomical phenes displayed stress and environmental plasticity; many phenotypic responses to water deficit were adaptive, and the magnitude of response varied by genotype. We identified 57 candidate genes associated with stress and environmental plasticity and 64 candidate genes associated with phenes under well‐watered and water‐stress conditions in Arizona and under well‐watered conditions in South Africa. Four candidate genes co‐localized between plasticity groups or for phenes expressed under each condition. The genetic architecture of phenotypic plasticity is highly quantitative, and many distinct genes control plasticity in response to water deficit and different environments, which poses a challenge for breeding programs.

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

“…We observed high heritability in root metaxylem phenes (Table 1). Broad-sense heritability observed was higher that previously reported values for root anatomical phenes (Kadam et al, 2017;Schneider et al, 2020a), but may be slightly conflated given that these values were based on only 95 genotypes than were planted in each season.Mean values of all metaxylem phenes apart from volumetric flow rate were unchanged in response to drought stress (Figure 1), but responses to drought varied by genotype (Supplemental Figure S1).…”

“…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).…”

“…Plasticity in xylem phenotypes in response to drought has been observed in maize (Klein et al, 2020; Schneider et al, 2020a), rice (Henry et al, 2012; Kadam et al, 2017), and wheat ( Triticum aestivum ) (Kadam et al, 2015), and are likely mediated by stress-responsive cellular and genetic factors. The genetic mechanisms underlying drought-induced variation in root xylem phenotypes are largely unknown.…”

Should Root Plasticity Be a Crop Breeding Target?

“…For example, in dicots tradeoffs exist between shallow and deep soil foraging (Ho et al, 2005). Recent studies suggest that plasticity is phenespecific and a single genotype may produce an adaptive plastic response for one phene and maladaptive plastic response for a different phene on the same plant (Schneider et al, 2020a).…”

“…To understand patterns of plasticity, we need to better understand and monitor local environments and changes in the environment. Subtle changes in the environment, such as localized nutrient patches, may induce a phenotypic response and if the environment is not carefully monitored, it makes interpretation of the plastic responses challenging (Schneider et al, 2020a). Field environments are often heterogeneous and difficult to monitor and replicate.…”