Root angle is controlled byEGT1in cereal crops employing an antigravitropic mechanism

Abstract

Root angle in crops represents a key trait for efficient capture of soil resources. Root angle is determined by competing gravitropic versus antigravitropic offset (AGO) mechanisms. Here we report a root angle regulatory gene termed ENHANCED GRAVITROPISM1 ( EGT1 ) that encodes a putative AGO component, whose loss-of-function enhances root gravitropism. Mutations in barley and wheat EGT1 genes confer a striking root phenotype, where every root class adopts a steeper growth angle. EGT1 encodes an F-box and Tubby domain-containing protein that is highly conserved across plant species. Haplotype analysis found that natural allelic variation at the barley EGT1 locus impacts root angle. Gravitropic assays indicated that Hvegt1 roots bend more rapidly than wild-type. Transcript profiling revealed Hvegt1 roots deregulate reactive oxygen species (ROS) homeostasis and cell wall-loosening enzymes and cofactors. ROS imaging shows that Hvegt1 root basal meristem and elongation zone tissues have reduced levels. Atomic force microscopy measurements detected elongating Hvegt1 root cortical cell walls are significantly less stiff than wild-type. In situ analysis identified HvEGT1 is expressed in elongating cortical and stele tissues, which are distinct from known root gravitropic perception and response tissues in the columella and epidermis, respectively. We propose that EGT1 controls root angle by regulating cell wall stiffness in elongating root cortical tissue, counteracting the gravitropic machinery’s known ability to bend the root via its outermost tissues. We conclude that root angle is controlled by EGT1 in cereal crops employing an antigravitropic mechanism.

ENHANCED GRAVITROPISM 2 coordinates molecular adaptations to gravistimulation in the elongation zone of barley roots

“…5g). These results suggest that gravitropism regulation of EGT2 might be similar to that of EGT1 , which was proposed to control cell wall stiffness by regulating peroxidase and cell wall loosening-related enzymes, therefore mediating AGO (Fusi et al ., 2022).…”

“…(Supporting Information Fig. S3e-g; Kawamoto et al ., 2020; Fusi et al ., 2022). Moreover, modules correlated only with wild type or egt2 at some time point after gravistimulation might be involved in EGT2 -independent or EGT2 -dependent gravitropism, respectively.…”

Phenotypic and Genotypic Diversity of Roots Response to Salt in Durum Wheat Seedlings

“…The root system remodeling strategies under adverse conditions is a great opportunity for adaptation and optimal development of the plant, as the first organ that senses and responds to abiotic stress, and then through efficient uptake of water and nutrients. Latest studies demonstrated that root system features, especially root angle in crop plants, play a main role in adapting to adverse conditions [ 20 , 22 , 37 ].…”

“…Genotypes under control conditions were distinguished regarding root angle into two groups, genotypes Vulci and Pelsodur with high salt-tolerant J. Khetifa had a narrower root angle than genotypes Sebatel, Azeghar, and Cham1. It was reported that root angle depends on plant root ability to control gravitropic versus anti-gravitropic mechanisms, which is the main factor in avoiding salty soil [ 20 , 21 , 22 ]. In this regard, root tips could be a good indicator for selection as they are involved in root gravity perception and regulation.…”

“…Moreover, it was reported that the roots of Arabidopsis exhibited reduced gravitropism under salt conditions to grow against the gravity vector [ 21 ]. In addition, the identified gene in cereal crops responsible for gravitropism versus anti-gravitropism regulatory mechanisms also controls the root angle [ 22 ]. The narrow root angle was determined as a very important feature in selecting genotypes for drought tolerance since genotypes with a narrow root angle can grow deeper compared with varieties with a wider root angle [ 23 , 24 , 25 ].…”