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

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.