Plant organ development is important for adaptation to a changing environment. Genetic and physiological studies have revealed that plant hormones play key roles in lateral root formation. In this study, we show that MIZU-KUSSEI1 (MIZ1), which was identified originally as a regulator of hydrotropism, functions as a novel regulator of hormonally mediated lateral root development. Overexpression of MIZ1 (MIZ1OE) in roots resulted in a reduced number of lateral roots being formed; however, this defect could be recovered with the application of auxin. Indole-3-acetic acid quantification analyses showed that free indole-3-acetic acid levels decreased in MIZ1OE roots, which indicates that alteration of auxin level is critical for the inhibition of lateral root formation in MIZ1OE plants. In addition, MIZ1 negatively regulates cytokinin sensitivity on root development. Application of cytokinin strongly induced the localization of MIZ1-green fluorescent protein to lateral root primordia, which suggests that the inhibition of lateral root development by MIZ1 occurs downstream of cytokinin signaling. Surprisingly, miz2, a weak allele of gnom, suppressed developmental defects in MIZ1OE plants. Taken together, these results suggest that MIZ1 plays a role in lateral root development by maintaining auxin levels and that its function requires GNOM activity. These data provide a molecular framework for auxin-dependent organ development in Arabidopsis (Arabidopsis thaliana).

The ter (teratoma) gene causes germ cell deficiency and a high incidence of congenital testicular teratomas derived from primordial germ cells in 129/Sv‐ter strain mice. Ovarian teratomas in LTXBJ mice originate from ovarian parthenotes. In order to study the function of the ter gene in germ cell development and teratocarcinogenesis, we examined the influence of a foreign genetic background on the ter action by introducing the ter gene of 129/Sv‐ter strain mice into C57BL/6J, LTXBJ and C3H/HeJ genetic backgrounds by the backcross method and by thus establishing B6‐ter, LTXBJ‐ter and C3H‐ter ter congenic strains, respectively. Histological analysis showed that germ cell deficiency occurred in both sexes of the ter mutants, through the fetal stages to adulthood, but that congenital testicular teratocarcinogenesis did not occur after the fifth backcross generation. The ter/ter gonads were smaller than normal (+/+ or +/ter). Experimental testicular teratomas never developed from intratesticular grafts of B6‐ter genital ridges. LTXBJ‐ter/ter females had no ovarian teratomas. It is concluded that the ter gene is solely responsible for germ cell deficiency, but not testicular teratocarcinogenesis, in ter congenic strains having background genes other than 129/Sv‐ter and that the ter gene is not involved in ovarian teratocarcinogenesis.

Cucumber (Cucumis sativus) seedlings grown in a horizontal position develop a specialized protuberance (or peg) on the lower side of the transition zone between the hypocotyl and the root. This occurs by suppressing peg formation on the upper side via a decrease in auxin resulting from a gravitational response. However, the gravity-stimulated mechanism of inducing asymmetric auxin distribution in the transition zone is poorly understood. The gravity-sensing tissue responsible for regulating auxin distribution in the transition zone is thought to be the endodermal cell. To characterize the gravity-stimulated mechanism, the auxin efflux facilitator PIN-FORMED1 (CsPIN1) in the endodermis was identified and the localization of CsPIN1 proteins during the gravimorphogenesis of cucumber seedlings was examined. Immunohistochemical analysis revealed that the accumulation pattern of CsPIN1 protein in the endodermal cells of the transition zone of cucumber seedlings grown horizontally differed from that of plants grown vertically. Gravistimulation for 30 min prompted changes in the accumulation pattern of CsPIN1 protein in the endodermis as well as the asymmetric distribution of auxin in the transition zone. Furthermore, 2,3,5-triiodobenzoic acid inhibited the differential distribution of auxin as well as changes in the accumulation pattern of CsPIN1 in the endodermis of the transition zone during gravistimulation. These results suggest that the altered pattern of CsPIN1 accumulation in the endodermis in response to gravistimulation influences lateral auxin transport through the endodermis, resulting in asymmetric auxin distribution in the transition zone.

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