Morphological, genetic and molecular characteristics of barley root hair mutants

Abstract

Root hairs are tubular outgrowths of specialized epidermal cells called trichoblasts. They affect anchoring plants in soil, the uptake of water and nutrients and are the sites of the interaction between plants and microorganisms. Nineteen root hair mutants of barley representing different stages of root hair development were subjected to detailed morphological and genetic analyses. Each mutant was monogenic and recessive. An allelism test revealed that nine loci were responsible for the mutated root hair phenotypes in the collection and 1–4 mutated allelic forms were identified at each locus. Genetic relationships between the genes responsible for different stages of root hair formation were established. The linkage groups of four loci rhl1, rhp1, rhi1 and rhs1, which had previously been mapped on chromosomes 7H, 1H, 6H and 5H, respectively, were enriched with new markers that flank the genes at a distance of 0.16 cM to 4.6 cM. The chromosomal position of three new genes – two that are responsible for the development of short root hairs (rhs2 and rhs3) and the gene that controls an irregular root hair pattern (rhi2) – were mapped on chromosomes 6H, 2H and 1H, respectively. A comparative analysis of the agrobotanical parameters between some mutants and their respective parental lines showed that mutations in genes responsible for root hair development had no effect on the agrobotanical performance of plants that were grown under controlled conditions. The presented mutant collection is a valuable tool for further identification of genes controlling root hair development in barley.Electronic supplementary materialThe online version of this article (doi:10.1007/s13353-014-0225-x) contains supplementary material, which is available to authorized users.

Root Hair Development in the Grasses: What We Already Know and What We Still Need to Know

“…In wild-type barley, symplasmic communication is limited to the root zone in which cells start to develop, whereas in the root-hairless mutant rhl1.b, all epidermal cells, even those in the mature zone of the root, remain interconnected; the absence of callose deposits in the plasmodesmata has been suggested as the basis for this difference (Marzec et al, 2014b). Apart from the allelic mutants that have been isolated in barley (Gahoonia et al, 2001;Chmielewska et al, 2014), hairless mutants have not as yet been obtained in the grasses. In rice and maize, some of the mutants that were classified previously as root hairless in fact develop very short RHs, while others exhibit bulges on the root that fail to develop into a recognizable RH (Hochholdinger et al, 2008;Yuo et al, 2009Yuo et al, , 2011.…”

“…Simultaneously, attempts have been made to uncover the molecular basis of RH development in the grasses at both the transcriptomic (Kwasniewski et al, 2010) and proteomic (Nestler et al, 2011;Janiak et al, 2012) levels. Mutants have provided an invaluable means for identifying the key genes that are involved in the various stages of RH formation as well as to validate conclusions that are based on large-scale analyses (Chmielewska et al, 2014). Meanwhile, histological analyses of cell modifications during RH development have led to a better understanding of the differentiation process (Kim and Dolan, 2011;Marzec et al, 2013Marzec et al, , 2014b.…”

“…The same authors further showed that the efficiency of water uptake is 55% higher in wildtype roots than in those of the hairless mutant brb, thus reflecting the large root surface available for water uptake. On the other hand, no water-deficient features were observed for the root-hairless mutants rhl1.a to rhl1.c when plants were grown under optimal conditions in a growth chamber (Chmielewska et al, 2014), giving the assumption that RHs are not essential for water uptake in well-watered soil. RH elongation is more pronounced in plants that are grown in dry soil than in those that do not experience any moisture stress.…”

Rhizosheath formation and involvement in foxtail millet (Setaria italica) root growth under drought stress

“…The Arabidopsis homolog of Seita.2G057800 ( At2G24260 ) complements the root‐hairless phenotype (Karas et al ). The maize homolog of Seita.8G104600 ( AY265854 ) encodes a SEC3‐like protein, which is a member of a putative exocyst complex that is required for normal exocytosis in the tip of root hairs during elongation (Wen et al ; Chmielewska et al ). Another upregulated root‐hair gene in foxtail millet, Seita.7G190800, is homologous to AY351786 in maize, which is required for root hair elongation.…”

Arabinogalactan proteins are involved in root hair development in barley

“…The analysis involved the following wild-type cultivars of barley ( Hordeum vulgare L.): Dema, Diva, Karat, and Optic, along with the root hair mutants rhl1.b , rhp1.a rhs1.a , rhs2.a , rhs.3a , and rhs4.a ( Table 2 ), all of which have been described by Chmielewska et al (2014) . Caryopses were surface sterilized by immersion in 20% household bleach and then germinated under aeroponic conditions in glass tubes sealed with Parafilm ( Szarejko et al , 2005 ) maintained under a 16h photoperiod (180 µEm –2 s –1 light) at 20°C for 5 days.…”