ENHANCED GRAVITROPISM 2encodes a STERILE ALPHA MOTIF–containing protein that controls root growth angle in barley and wheat

Abstract

The root growth angle defines how roots grow toward the gravity vector and is among the most important determinants of root system architecture. It controls water uptake capacity, nutrient use efficiency, stress resilience, and, as a consequence, yield of crop plants. We demonstrated that the egt2 (enhanced gravitropism 2) mutant of barley exhibits steeper root growth of seminal and lateral roots and an auxin-independent higher responsiveness to gravity compared to wild-type plants. We cloned the EGT2 gene by a combination of bulked-segregant analysis and whole genome sequencing. Subsequent validation experiments by an independent CRISPR/Cas9 mutant allele demonstrated that egt2 encodes a STERILE ALPHA MOTIF domain–containing protein. In situ hybridization experiments illustrated that EGT2 is expressed from the root cap to the elongation zone. We demonstrated the evolutionary conserved role of EGT2 in root growth angle control between barley and wheat by knocking out the EGT2 orthologs in the A and B genomes of tetraploid durum wheat. By combining laser capture microdissection with RNA sequencing, we observed that seven expansin genes were transcriptionally down-regulated in the elongation zone. This is consistent with a role of EGT2 in this region of the root where the effect of gravity sensing is executed by differential cell elongation. Our findings suggest that EGT2 is an evolutionary conserved regulator of root growth angle in barley and wheat that could be a valuable target for root-based crop improvement strategies in cereals.

Root angle is controlled byEGT1in cereal crops employing an antigravitropic mechanism

“…Kirschner et al. ( 41 ) recently reported a barley mutant with a steeper root growth angle phenotype termed ENHANCED GRAVITROPISM 2 (EGT2), whose wild-type gene encoded a STERILE ALPHA MOTIVE-containing protein and also deregulates cell wall-related genes. Although EGT1 and EGT2 both function in auxin independent AGO mechanisms, they are expressed in distinct tissue types and target different set of cell wall genes.…”

Root system architecture in cereals: progress, challenges and perspective

“…Along with advances in root phenotyping, considerable progress has been made in acquiring knowledge about the genetic modulation of RSA. Genetic and transcriptomics approaches have revealed a plethora of cereal genes like DRO1 , RSL4 , RMD (Huang et al., 2018) and Egt2 (Kirschner et al., 2021) that can effectively modulate the structure and molecular functions of root architecture. How these genetic factors are regulated by synchronously acting environmental cues remains enigmatic.…”

Enhancing cereal productivity by genetic modification of root architecture

“…Target gene a Function Root-associated parameters Downstream elements barley EGT2 [117] SAM domain-containing protein narrower seminal root and LR angle, deeper root rice RopGEF3 [121] GTP-binding protein shorter root hair rice LPR5 [122] Ferroxidase involved in Pi homeostasis reduced primary root length member, with one specifically targeting the F-box coding region. [104] The rice OsTIR1/AFB homologous genes possess partially overlapping functions in diverse developmental processes.…”

“…[14] It was shown that the root angle is regulated by ENHANCED GRAVITROPISM2 (EGT2) gene, which is conserved in barley and wheat, and that EGT2 acts in an auxin-independent manner. [117] Moreover, the authors suggest that more genes with function in the regulation of RGA could be identified in the future. [86,117] As DRO1family genes and the EGT2 gene have a specified role in RGA without adverse effects on other morphological traits, they could be very promising genome editing targets for improving the tolerance to various abiotic stress factors.…”

“…[117] Moreover, the authors suggest that more genes with function in the regulation of RGA could be identified in the future. [86,117] As DRO1family genes and the EGT2 gene have a specified role in RGA without adverse effects on other morphological traits, they could be very promising genome editing targets for improving the tolerance to various abiotic stress factors. It would be interesting to transfer the knowledge to other cereal crops and test their response to different stress factors.…”