Phototropin 1 (phot1) and phot2, which are blue light receptor kinases, function in blue light-induced hypocotyl phototropism, chloroplast relocation, and stomatal opening in Arabidopsis (Arabidopsis thaliana). Previous studies have shown that the proteins RPT2 (for ROOT PHOTOTROPISM2) and NPH3 (for NONPHOTOTROPIC HYPOCOTYL3) transduce signals downstream of phototropins to induce the phototropic response. However, the involvement of RPT2 and NPH3 in stomatal opening and in chloroplast relocation mediated by phot1 and phot2 was unknown. Genetic analysis of the rpt2 mutant and of a series of double mutants indicates that RPT2 is involved in the phot1-induced phototropic response and stomatal opening but not in chloroplast relocation or phot2-induced movements. Biochemical analyses indicate that RPT2 is purified in the crude microsomal fraction, as well as phot1 and NPH3, and that RPT2 makes a complex with phot1 in vivo. On the other hand, NPH3 is not necessary for stomatal opening or chloroplast relocation. Thus, these results suggest that phot1 and phot2 choose different signal transducers to induce three responses: phototropic response of hypocotyl, stomatal opening, and chloroplast relocation.

SummarypMADS3, a petunia class C gene, is the candidate homologue of Arabidopsis AGAMOUS (AG), which is involved in the specification of stamens and carpels. We report the characterization of loss-of-function phenotype of pMADS3 that resulted from silencing of this gene. Silencing of pMADS3 resulted in homeotic conversion of stamens into petaloid structures, whereas the carpels were only weakly affected. Ectopic secondary inflorescences emerged from the interstamenal region in the third whorl, which is unique and has not been reported for any class C gene of other plant species. Third-order inflorescences emerged at corresponding positions in the third whorl of inner flowers of secondary inflorescences, indicating reiterative conversion of parts of the floral meristem into inflorescence meristem. On the basis of phenotypic analysis of the pMADS3-silenced plants, we propose that pMADS3 is involved in determination of floral organ and floral meristem identity in petunia. Two hybrid studies in yeast showed that PMADS3 protein interacted specifically with FBP2, a candidate homologue of Arabidopsis SEPALLATA3 (SEP3). The evidence presented here suggest that a complex involving PMADS3 and FBP2 is responsible for specification of organ identity in the third whorl.

Background: GREEN PETAL (GP) is thought to be a petunia class B¯oral homeotic gene, because the gp mutant¯ower displays a severe homeotic conversion of petals into sepals in the second whorl. However, since the third whorl stamens remain unaffected in the gp null mutant, gp is different from class B mutants in Arabidopsis and Antirrhinum, which also show a conversion of the third whorl stamens into the carpelloid tissue. BLIND (BL) is thought to be a petunia class A¯oral homeotic gene, because the bl mutant¯ower displays homeotic conversions of sepals into the stigmatoid tissue in the ®rst whorl and of the corolla limb into antheroid structures in the second whorl.

;The Arabidopsis CURLY LEAF (CLF) gene is required to repress transcription of the class C gene AGAMOUS (AG) in whorls 1 and 2 of flowers and also in vegetative organs. CLF encodes a protein with homology to the product of the Drosophila Polycomb-group gene Enhancer of zeste [E(z)], which is involved in embyogenesis. In this study, we isolated three petunia CLF-like genes (PhCLF1, PhCLF2 and PhCLF3) based on the sequence homology between CLF and E(Z). Sequence analysis suggests that PhCLF1 and PhCLF2 are orthologs of CLF, whereas PhCLF3 is an ortholog of the Arabidopsis gene EZA1. We identified several conserved domains among products of PhCLF genes and related genes. PhCLF1 and PhCLF2 were expressed in all floral organs and leaves. The PhCLF1 transcripts were accumulated especially in corolla limbs, and contained several alternatively spliced RNA species. PhCLF1 and PhCLF2 do not appear to be the BLIND gene, which is required to repress transcription of the petunia class C gene, but their expression was affected by the homeotic conversion of organs in the blind flower. Our findings show that expression of PhCLF1 is regulated differently from that of PhCLF2, and suggest that the two petunia CLF orthologs function differently from each other.

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