ASSEMBLING A COLLECTION OF ROOT HAIR MUTANTS IN BARLEY (HORDEUM VULGARE)

Root hairs are crucial for crop plants, significantly enhancing their ability to absorb soil and water resources and contributing to several other functional traits. Root hairs contribute to nutrient foraging not only by expanding the root surface area but also by increasing mucilage exudation and the diffusion of compounds like citrate or acid phosphatase, and by shaping the rhizospheric microbiota. The molecular genetic control of root hair development in cereals and specifically in barley is still largely unknown. This study aimed to screen the TILLMore mutant collection for root hair phenotypes using a novel CD-case-based protocol. So far, we have screened ca.1,200 lines and identified 13 root hair mutants that were grouped into: root hairless (three mutant lines), defective root hairs in early developmental stage (two mutant lines), short root hairs (six mutant lines), few root hairs (one mutant lines) and one line that displayed a root hairless/defective early-stage phenotype in seminal roots but showed wild-type root hairs in lateral and crown roots. The genetic control of the root hairless TILLMore line TM1291 was investigated in more details. TM1291 exhibited a consistent root hairless phenotype across all root types (seminal, lateral, and crown). The F1 plants obtained from the TM1291 × Barke showed shorter root hair than Barke, suggesting incomplete dominance. Observation on the F2 population obtained from selfing the same F1 plants confirmed that the TM1291 root hairless trait is governed by a single locus, with an incompletely dominant allele donated by TM1291, with a 1:2:1 segregation ratio. The causal gene was cloned through mapping by sequencing and shown to map on chromosome 7 and to correspond to H. vulgare ROOT HAIRLESS 1 (Hvrhl1), encoding a transcription factor already known to be involved in root hair development. This transcription factor comprises two distinct functional domains, namely the bHLH and the LRL domains, and TM1291 was shown to carry a novel allele characterized by an amino acid substitution in the conserved bHLH domain. These results confirm that the TILLMore root hair defective mutant collection has the potential to shed light on the molecular genetic control of root hair development and promises to contribute in the long term to select more resilient cultivars, better adapted to sustainable cropping systems. Funded by the European Union - NextGenerationEU under the National Recovery and Resilience Plan (PNRR) - Mission 4 Education and research - Component 2 From research to business - Investment 1.1 Notice PRIN 2022 PNRR (DD N. 1409 del 14/09/2022), project title: iSMARTBAR - Identifying geneS to iMprove cAnopy aRchitecture and phoTosynthesis for future-proof BARley, proposal code: P20224STA9, CUP J53D2301819000.