Strigolactones (SLs) have recently been found to regulate shoot branching, but the functions of SLs at other stages of development and the regulation of SL-related gene expression are mostly unknown in Arabidopsis. In this study, we performed real-time reverse transcription-PCR (RT-PCR) and microarray analysis using wild-type plants and SL-deficient/insensitive mutants to understand the molecular mechanisms underlying SL biosynthesis and signaling. We found that there is responsiveness to SL in the gene expression of Arabidopsis seedlings, which includes feedback regulation of two carotenoid cleavage dioxygenase genes. Microarray analysis revealed that exogenously applied SL regulated the expression of several genes, including light signaling-related genes and auxin-inducible genes. We also found that MORE AXILLARY GROWTH (MAX)2 plays an important role in the expression of SL-regulated genes. Our data support previous studies indicating that SL might function at the seedling stage. Analysis of SL-responsive and MAX2 downstream gene candidates provides new opportunities to broaden our understanding of SL signaling.

The glycosylated forms of abscisic acid (ABA) have been identified from many plant species and are known to be the forms of ABA-catabolism, although their (physiological) roles have not yet been elucidated. ABA-glucosyltransferase (-GTase) is thought to play a key role in the glycosylation of ABA. We isolated an ABA-inducible GTase gene from UDP-GTase homologs obtained from adzuki bean (Vigna angularis) seedlings. The deduced amino acid sequence (accession no. AB065190) showed 30% to 44% identity with the known UDP-GTase homologs. The recombinant protein with a glutathioneS-transferase-tag was expressed in Escherichia coli and showed enzymatic activity in an ABA-specific manner. The enzymatic activity was detected over a wide pH range from 5.0 to 9.0, the optimum range being between pH 6.0 and 7.3, in a citrate and Tris-HCl buffer. The product from racemic ABA and UDP-d-glucose was identified to be ABA-GE by gas chromatography/mass spectrometry. The recombinant GTase (rAOG) converted 2-trans-(+)-ABA better than (+)-S-ABA and (−)-R-ABA. Although trans-cinnamic acid was slightly converted to its conjugate by the GTase, (−)-PA was not at all. The mRNA level was increased by ABA application or by water stress and wounding. We suggest that the gene encodes an ABA-specific GTase and that its expression is regulated by environmental stress.

Summary: A variety of insect species induce galls on host plants. Several studies have implicated phytohormones in insect‐induced gall formation. However, it has not been determined whether insects can synthesize phytohormones. It has also never been established that phytohormones function in gall tissues. Liquid chromatography and tandem mass spectrometry (LC/MS/MS) were used to analyse concentrations of endogenous cytokinins and the active auxinIAAin the gall‐inducing sawfly (Pontaniasp.) and its host plant,Salix japonica. Feeding experiments demonstrated the ability of sawfly larvae to synthesizeIAAfrom tryptophan. Gene expression analysis was used to characterize hormonal signalling in galls. Sawfly larvae contain high concentrations ofIAAandt‐zeatin, and produceIAAfrom tryptophan. The glands of adult sawflies, the contents of which are injected into leaves upon oviposition and are involved in the initial stages of gall formation, contain an extraordinarily high concentration oft‐zeatin riboside. Transcript levels of some auxin‐ and cytokinin‐responsive genes are significantly higher in gall tissue than in leaves. The abnormally high concentration oft‐zeatin riboside in the glands strongly suggests that the sawfly can synthesize cytokinins as well asIAA. Gene expression profiles indicate high levels of auxin and cytokinin activities in growing galls.

In plants, gibberellin (GA)-responding mutants have been used as tools to identify the genes that control specific steps in the GA-biosynthetic pathway. They have also been used to determine which native GAs are active per se, i.e., further metabolism is not necessary for bioactivity. We present metabolic evidence that the D1 gene of maize (Zea mays L.) controls the three biosynthetic steps: GA20 to GA1, Ga20 to GA5, and GA5 to GA3. We also present evidence that three gibberellins, GA1, GA5, and GA3, have per se activity in stimulating shoot elongation in maize. The metabolic evidence comes from the injection of [17-13C,3H]GA20 and [17-13C,3H]GA5 into seedlings of d1 and controls (normal and d5), followed by isolation and identification of the 13C-labeled metabolites by full-scan GC-MS and Kovats retention index. For the controls, GA20 was metabolized to GA1,GA3, and GA5; GA5 was metabolized to GA3. For the d1 mutant, GA20 was not metabolized to GA1, GA3, or to GA5, and GA5 was not metabolized to GA3. The bioassay evidence is based on dosage response curves using d1 seedlings for assay. GA1, GA3, and GA5 had similar bioactivities, and they were 10-times more active than GA20.

Early nodulin-like proteins (ENODLs) are chimeric arabinogalactan proteins (AGPs) related to the phytocyanin family. Although they show similarities with other phytocyanins, they lack amino acid residues for copper binding. Despite the existence of other phytocyanins, information about the function of ENODLs in plants is largely lacking. In this study, we characterized ENODL genes consisting of 22 members in Arabidopsis thaliana. Structure prediction indicated that most ENODLs are glycosylphosphatidylinositol-anchored chimeric AGPs. Expression analysis by real-time reverse transcription polymerase chain reaction indicated that most ENODL genes showed spatially specific expression, mainly in the flower organs. Furthermore, we obtained and analyzed 26 homozygous T-DNA insertion lines of 15 ENODL genes, but novel biological roles were not uncovered, probably due to functional redundancy. The detailed phylogenetic and expression analyses and characterization of the available insertion lines in this study might facilitate future studies to elucidate the biological roles of ENODLs.

Fluorescence differential display was used to isolate the gibberellin (GA)-responsive gene, CsAGP1, from cucumber (Cucumis sativus) hypocotyls. A sequence analysis ofCsAGP1 indicated that the gene putatively encodes a “classical” arabinogalactan protein (AGP) in cucumber. Transgenic tobacco (Nicotiana tabacum) plants overexpressingCsAGP1 under the control of the cauliflower mosaic virus 35S promoter produced a Y(βGlc)₃-reactive proteoglycan in addition to AGPs present in wild-type tobacco plants. Immuno-dot blotting of the product, using anti-AGP antibodies, showed that the CsAGP1 protein had the AGP epitopes common to AGP families. The transcription level of CsAGP1 in cucumber hypocotyls increased in response not only to GA but also to indole-3-acetic acid. Although CsAGP1 is expressed in most vegetative tissues of cucumber, including the shoot apices and roots, the GA treatment resulted in an increase in the mRNA level of CsAGP1 only in the upper part of the hypocotyls. Y(βGlc)₃, which selectively binds AGPs, inhibited the hormone-promoted elongation of cucumber seedling hypocotyls. Transgenic plants ectopically expressingCsAGP1 showed a taller stature and earlier flowering than the wild-type plants. These observations suggest thatCsAGP1 is involved in stem elongation.