Functional analysis of barley HvRTH3 reveals its role in root hair patterning with no detectable impact on drought...

Root hairs, tubular extensions of the rhizodermal cells, facilitate nutrient uptake, yet their role in water acquisition remains debated and may be species- and soil-specific. To elucidate the genetic basis of root hair development and assess their physiological relevance in barley (Hordeum vulgare L.), particularly under water-limited conditions, we characterized a mutant with a changed root hairs phenotype. The HvRTH3 gene, a barley homolog of the maize COBRA gene roothairless3 (rth3) encoding a COBRA protein (Hochholdinger et al., 2008), was subjected to TILLING analysis. In the hvrth3.h mutant, the mutation was identified in 804 bp position (transition of G to A), which results in premature STOP codon, that caused a reduction of protein length by 405 aa. The sparsely located root hairs in a barley hvrth3.h mutant, otherwise than in maize, where short root hairs were observed, was a result of a smaller number of trichoblasts in comparison to WT. The newly identified hvrth3.h mutant was not allelic to any characterized barley mutant isolated in our lab. It showed diminished root traits and yield under greenhouse and field conditions but did not exhibit pronounced disadvantage under severe drought. The expression of HvRTH3 gene was observed in all analyzed tissues, with the highest expression level in root elongation zone. HvRTH3 is essential for root hair development, but apparently dispensable for water uptake under severe drought.