Abstract
In vascular plants, lateral root (LR) formation is critical for the development of the root architecture. To get insight into the mechanisms of LR formation, we identified the fewer roots (fwr) mutant with a decreased number of LRs in Arabidopsis. The fwr mutation is a single recessive and strongly reduces the frequency of LR formation. The fwr mutant was less sensitive to exogenous auxins that induced LR formation. Fine mapping and sequence analysis revealed that the fwr has a missense mutation in the GNOM gene, encoding an ARF-GEF that functions in vesicle trafficking. This was confirmed by the allelism test between the fwr and GNOM T-DNA insertion mutant. GNOM is required for the establishment of the apical-basal axis during embryogenesis and acts during auxin-mediated growth and development by affecting the intracellular location of PIN1, an auxin efflux carrier. Although several types of gnom mutant alleles with embryonic or seedling lethality are known, few mutants that are specifically defective in LR formation have been reported. We will discuss the role of GNOM in LR formation, based on phenotypic analysis of the fwr mutant.
