Preliminary Study Of The Adventitious Root Development-related Mutant Karl2

Rice is one of the most important food crops worldwide. Its root system consists of one primary root and a mass of adventitious roots (AR). Although the morphology and physiology of adventitious root have been well studied, little is known about the molecular regulators for adventitious root development in rice. By screening a rice EMS-generated mutant library (Kasalath, indica), we isolated a mutant with delayed development of adventitious root, designated as karl2. The phenotypic, physiological and genetic characterizations of karl2 were investigated. The results are summarized as follows:1. The karl2 (Kasalath adventitious rootless2) mutant seedlings defected adventitousroot(AR) within five days after germination and the number of AR of the mutant was significantly less than the wild type (WT) during the growth period. Cross-sections at the base of the stem of 4d-old seedlings showed that the formation of adventitious root primordium was impaired in the karl2 mutant. The lateral roots (LR) of the mutants were also less than the WT on the primary root, but no significant difference in the average length of LR between the mutant and WT. The primary root of karl2 was significantly longer than that of WT in the first 3 weeks while the shoot was lower.2. karl2 showed similar response with the wild type to different concentrations of IAAand 6-BA. The elongation of primary root of karl2 was more sensitive to ACC treatment than wild type, and more resistant to nitrate silver. Auxin and ethylene could induce the development of adventitious roots in karl2 within the early time.3. Genetic analysis with reciprocal crosses between karl2 and wild-type plants indicated that karl2 possessed a dominant mutation in a single nuclear locus.4. The KARl2 gene was mapped between RM6151 and S02-2049K on chromosome 2within a region about 100K bp.