DISRUPTION OF INTERFASCICULAR FIBER DIFFERENTIATION IN AN ARABIDOPSISMUTANT

Arabidopsis develops interfascicular fibers in stems for needed suppor t of shoots. To study the molecular mechanisms controlling fiber diffe rentiation, we isolated an interfascicular fiber mutant (ifl1) by scre ening ethyl methanesulfonate-mutagenized Arabidopsis populations. This mutant lacks normal interfascicular fibers in stems. Interestingly, s ome interfascicular cells were sclerified in the upper parts but not i n the basal parts of the ifl1 stems. These sclerified cells were diffe rentiated at a position different from that of interfascicular fibers in the wild type. Lack of interfascicular fibers correlated with a dra matic change of stem strength. Stems of the mutant could not stand ere ct and were easily broken by bending. Quantitative measurement showed that it took approximately six times less force to break basal stems o f the mutant than of the wild type. In addition, noticeable morphologi cal changes were asssociated with the mutant, including long stems, da rk green leaves with delayed senescence, and reduced numbers of caulin e leaves and branches. Genetic analysis showed that the ifl1 mutation was monogenic and recessive. The ifl1 locus was mapped to a region bet ween the 17C2 and 7H9L markers on chromosome 5. Isolation of the ifl1 mutant provides a novel means to study the genetic control of fiber di fferentiation.