Root hairless 2 (rth2) mutant represents a loss-of-function allele of the cellulose synthase-like gene OsCSLD1 in rice (Oryza sativa L.)

Abstract

Root hair is considered to play important roles in water and nutrient uptake and anchoring the plant to the soil. To gain further knowledge of root hair morphogenesis in rice, we isolated root hairless 2 (rth2) mutant from the mutant panel of Nipponbare. Positional cloning and complementation test revealed that the causal gene of rth2 was Cellulose Synthase-Like D1 (OsCSLD1). rth2 has a premature stop codon in exon 1 as a result of two consecutive nucleotide substitutions and is predicted to produce truncated proteins lacking the D, D, D, QxxRW motif and 8 transmembrane domains. In rth2, bulges were normally initiated from asymmetric divisions of root epidermal cells, but bulges did not elongate. Therefore, rth2 shows completely roothairless phenotype. qRT-PCR analysis revealed that OsCSLD1 was expressed not only in root but also in shoot. In situ hybridization showed that OsCSLD1 was expressed not only in root hairs but also in epidermal and cortex cell walls except for stele. Agronomic character evaluation in pot experiments showed that rth2 did not differ significantly from Nipponbare in all characters examined except for root dry weight, which showed a significant increase in rth2. In paddy field experiment, rth2 was significantly inferior compared with Nipponbare in agronomic performance.

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

“…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.…”

“…The earliest reported involvement of cellulose synthase in RH elongation in the grasses relates to the product of OsCSLD1, a rice gene that encodes a cellulose synthase-like D1 protein (Kim et al, 2007). This gene is expressed throughout the plant as well as in trichoblasts, atrichoblasts, and root cortex cells (Yuo et al, 2011). A Dissociation element (Ds) insertion mutant suffered a 65% to 75% reduction in RH length but no difference in RH density or distribution, which was taken to imply a role for OsCSLD1 in RH elongation.…”

“…Confirmation was obtained from the behavior of an OsCSLD1 overexpressor, which produced RHs that were double the length of those developed by wild-type plants ( Kim et al, 2007). A second rice mutant, termed rth2, was shown to be a loss-of-function allele of OsCSLD1 (Yuo et al, 2011). Unlike those of the Ds insertion mutant, rth2 roots fail to develop bulges on the root surface.…”

“…A similar situation occurs in Arabidopsis, where a mutated form of the ubiquitously expressed gene CSLD3 severely inhibits RH elongation, although it does not compromise the formation of the bulge (Wang et al, 2001). Defects in OsCLDS1 or AtCSLD3 are generally complemented by various paralogs, although this is not the case for the development of RHs (Yuo et al, 2011). Moreover, a mutation in the OsXXT1 gene, encoding xyloglucan 6-xylosytransferase, results in abnormal RH elongation.…”

Morphological, genetic and molecular characteristics of barley root hair mutants

“…Despite the different mechanism of trichoblast differentiation, it is likely that root hair development in monocots may be similar to Arabidopsis . However, in the case of monocots, there are only a few reports on the isolation of root hair mutants: in barley ( Hordeum vulgare ; Gahoonia et al 2001 ; Engvild and Rasmussen, 2004 ; Kwasniewski and Szarejko, 2006 ; Janiak and Szarejko, 2007 ), in maize ( Zea mays ; Wen and Schnable, 1994 ; Wen et al 2005 ; Hochholdinger et al 2008 ) and in rice ( Oryza sativa ; Suzuki et al 2003 ; Kim et al 2007 ; Ding et al 2009 ; Yuo et al 2009 ; Yuo et al 2011 ; Huang et al 2013a , b ). Moreover, only a few genes have been identified at the molecular level (Wen et al 2005 ; Kim et al 2007 ; Hochholdinger et al 2008 ; Yuo et al 2009 ; Yuo et al 2011 ; Huang et al 2013a , b ).…”