Functional Analysis Of OsXXT1 Gene In Root Hair Development & Transposition Of Retrotransposon TOS17 In Rice

Root hairs are long tubular-shaped outgrowths from root epidermal cells. It vastly increases the root surface area that aid plants in nutrient acquisition, anchorage, and microbe interactions. Previously, we have screened a short root hair mutant, named as ksrh2 (kasalath short root hair 2).The mutant exhibited a significant short root hairs than wild type plants grown hydroponically. In this study, we further revealed that root hairs growth of ksrh2 were greatly inhibited and formed bubble-like extrusions at the tip of root hairs grown in acidic MS medium (pH4.5). At this growth condition, irregular epidermal cells of the meristion region were observed in ksrh2 by transverse section. These results suggested that the strength of cell wall may decrease in the mutant.Map based cloning showed that ksrh2 encodes a rice xylogucan xylosyltrasferase gene (OsXXT1). A base substitution of the ksrh2 mutant sequence switched Gly into Arg in the highly conserved glycosyltransferase domain, which may diminish the fuction of OsXXT1. By introducing a wild type OsXXT1 sequence into ksrh2, we successfully restored the short root hair phenotype of ksrh2.Microarray data show that OsXXT1 constitutively expressed in almost all tissues. To further analzing the expression pattern of OsXXT1, six independent OsXXT1 :GUS transgenic lines were obtained. GUS expression was observed in all major organs including callus, root tips, lateral root, leaves, panicles and inflorescences. Sections of roots showed that the GUS expression was mainly in epidermal cells of meristem region. This result also surpport the transversal sections of mature roots data.In addition, characteristics of retrotransposon TOS17 were analzyed in the rice cultivars Nipponbare and Shishoubaimao. Shishoubaimao has three original copies of TOS17. It was actived under tissue culture condition, and the copy number increased with the time of incubation. Suspension culture process resulted in more copies than that in solid culture. We proposed that a 3- to 4-month suspension tissue culture may be the optimal condition for producing a TOS17 insertion mutant library in Shishoubaimao.