Alteration of auxin polar transport in the Arabidopsis ifl1 mutants

The INTEXFASCICULAR FIBERLESS/REVOLUTA (IFL1/REV) gene is essential for the normal differentiation of interfascicular fibers and secondary xylem in th e inflorescence stems of Arabidopsis. It has been proposed that IFL1/REV in fluences auxin polar flow or the transduction of auxin signal, which is req uired for fiber and vascular differentiation. Assay of auxin polar transpor t showed that the ifl1 mutations dramatically reduced auxin polar flow alon g the inflorescence stems and in the hypocotyls. The null mutant allele ifl 1-2 was accompanied by a significant decrease in the expression level of tw o putative auxin efflux carriers. The ifl1 mutants remained sensitive to au xin and an auxin transport inhibitor. The ifl1-2 mutant exhibited visible p henotypes associated with defects in auxin polar transport such as pin-like inflorescence, reduced numbers of cauline branches, reduced numbers of sec ondary rosette inflorescence, and dark green leaves with delayed senescence . The visible phenotypes displayed by the ifl1 mutants could be mimicked by treatment of wild-type plants with an auxin polar transport inhibitor. In addition, the auxin polar transport inhibitor altered the normal differenti ation of interfascicular fibers in the inflorescence stems of wild-type Ara bidopsis. Taken together, these results suggest a correlation between the r educed auxin polar transport and the alteration of cell differentiation and morphology in the ifl1 mutants.