Determination of the motif responsible for interaction between the rice APETALA1/AGAMOUS-LIKE9 family proteins using a yeast two-hybrid system.
(9/1627)
A MADS family gene, OsMADS6, was isolated from a rice (Oryza sativa L.) young flower cDNA library using OsAMDS1 as a probe. With this clone, various MADS box genes that encode for protein-to-protein interaction partners of the OsMADS6 protein were isolated by the yeast two-hybrid screening method. On the basis of sequence homology, OsMADS6 and the selected partners can be classified in the APETALA1/AGAMOUS-LIKE9 (AP1/AGL9) family. One of the interaction partners, OsMADS14, was selected for further study. Both genes began expression at early stages of flower development, and their expression was extended into the later stages. In mature flowers the OsMADS6 transcript was detectable in lodicules and also weakly in sterile lemmas and carpels, whereas the OsMADS14 transcript was detectable in sterile lemmas, paleas/lemmas, stamens, and carpels. Using the yeast two-hybrid system, we demonstrated that the region containing of the 109th to 137th amino acid residues of OsMADS6 is indispensable in the interaction with OsMADS14. Site-directed mutation analysis revealed that the four periodical leucine residues within the region are essential for this interaction. Furthermore, it was shown that the 14 amino acid residues located immediately downstream of the K domain enhance the interaction, and that the two leucine residues within this region play an important role in that enhancement. (+info)
Molecular analysis of the anthocyanin2 gene of petunia and its role in the evolution of flower color.
(10/1627)
The shape and color of flowers are important for plant reproduction because they attract pollinators such as insects and birds. Therefore, it is thought that alterations in these traits may result in the attraction of different pollinators, genetic isolation, and ultimately, (sympatric) speciation. Petunia integrifolia and P. axillaris bear flowers with different shapes and colors that appear to be visited by different insects. The anthocyanin2 (an2) locus, a regulator of the anthocyanin biosynthetic pathway, is the main determinant of color differences. Here, we report an analysis of molecular events at the an2 locus that occur during Petunia spp evolution. We isolated an2 by transposon tagging and found that it encodes a MYB domain protein, indicating that it is a transcription factor. Analysis of P. axillaris subspecies with white flowers showed that they contain an2(-) alleles with two alternative frameshifts at one site, apparently caused by the insertion and subsequent excision of a transposon. A third an2(-) allele has a nonsense mutation elsewhere, indicating that it arose independently. The distribution of polymorphisms in an2(-) alleles suggests that the loss of an2 function and the consequent changes in floral color were not the primary cause for genetic separation of P. integrifolia and P. axillaris. Rather, they were events that occurred late in the speciation process, possibly to reinforce genetic isolation and complete speciation. (+info)
S-methylmethionine plays a major role in phloem sulfur transport and is synthesized by a novel type of methyltransferase.
(11/1627)
All flowering plants produce S-methylmethionine (SMM) from Met and have a separate mechanism to convert SMM back to Met. The functions of SMM and the reasons for its interconversion with Met are not known. In this study, by using the aphid stylet collection method together with mass spectral and radiolabeling analyses, we established that l-SMM is a major constituent of the phloem sap moving to wheat ears. The SMM level in the phloem ( approximately 2% of free amino acids) was 1.5-fold that of glutathione, indicating that SMM could contribute approximately half the sulfur needed for grain protein synthesis. Similarly, l-SMM was a prominently labeled product in phloem exudates obtained by EDTA treatment of detached leaves from plants of the Poaceae, Fabaceae, Asteraceae, Brassicaceae, and Cucurbitaceae that were given l-(35)S-Met. cDNA clones for the enzyme that catalyzes SMM synthesis (S-adenosylMet:Met S-methyltransferase; EC 2.1.1.12) were isolated from Wollastonia biflora, maize, and Arabidopsis. The deduced amino acid sequences revealed the expected methyltransferase domain ( approximately 300 residues at the N terminus), plus an 800-residue C-terminal region sharing significant similarity with aminotransferases and other pyridoxal 5'-phosphate-dependent enzymes. These results indicate that SMM has a previously unrecognized but often major role in sulfur transport in flowering plants and that evolution of SMM synthesis in this group involved a gene fusion event. The resulting bipartite enzyme is unlike any other known methyltransferase. (+info)
Regional expression of the rice KN1-type homeobox gene family during embryo, shoot, and flower development.
(12/1627)
We report the isolation, sequence, and pattern of gene expression of members of the KNOTTED1 (KN1)-type class 1 homeobox gene family from rice. Phylogenetic analysis and mapping of the rice genome revealed that all of the rice homeobox genes that we have isolated have one or two direct homologs in maize. Of the homeobox genes that we tested, all exhibited expression in a restricted region of the embryo that defines the position at which the shoot apical meristem (SAM) would eventually develop, prior to visible organ formation. Several distinct spatial and temporal expression patterns were observed for the different genes in this region. After shoot formation, the expression patterns of these homeobox genes were variable in the region of the SAM. These results suggest that the rice KN1-type class 1 homeobox genes function cooperatively to establish the SAM before shoot formation and that after shoot formation, their functions differ. (+info)
Arabidopsis alcohol dehydrogenase expression in both shoots and roots is conditioned by root growth environment.
(13/1627)
It is widely accepted that the Arabidopsis Adh (alcohol dehydrogenase) gene is constitutively expressed at low levels in the roots of young plants grown on agar media, and that the expression level is greatly induced by anoxic or hypoxic stresses. We questioned whether the agar medium itself created an anaerobic environment for the roots upon their growing into the gel. beta-Glucuronidase (GUS) expression driven by the Adh promoter was examined by growing transgenic Arabidopsis plants in different growing systems. Whereas roots grown on horizontal-positioned plates showed high Adh/GUS expression levels, roots from vertical-positioned plates had no Adh/GUS expression. Additional results indicate that growth on vertical plates closely mimics the Adh/GUS expression observed for soil-grown seedlings, and that growth on horizontal plates results in induction of high Adh/GUS expression that is consistent with hypoxic or anoxic conditions within the agar of the root zone. Adh/GUS expression in the shoot apex is also highly induced by root penetration of the agar medium. This induction of Adh/GUS in shoot apex and roots is due, at least in part, to mechanisms involving Ca2+ signal transduction. (+info)
Auxin-induced K+ channel expression represents an essential step in coleoptile growth and gravitropism.
(14/1627)
Auxin-induced growth of coleoptiles depends on the presence of potassium and is suppressed by K+ channel blockers. To evaluate the role of K+ channels in auxin-mediated growth, we isolated and functionally expressed ZMK1 and ZMK2 (Zea mays K+ channel 1 and 2), two potassium channels from maize coleoptiles. In growth experiments, the time course of auxin-induced expression of ZMK1 coincided with the kinetics of coleoptile elongation. Upon gravistimulation of maize seedlings, ZMK1 expression followed the gravitropic-induced auxin redistribution. K+ channel expression increased even before a bending of the coleoptile was observed. The transcript level of ZMK2, expressed in vascular tissue, was not affected by auxin. In patch-clamp studies on coleoptile protoplasts, auxin increased K+ channel density while leaving channel properties unaffected. Thus, we conclude that coleoptile growth depends on the transcriptional up-regulation of ZMK1, an inwardly rectifying K+ channel expressed in the nonvascular tissue of this organ. (+info)
Application of mass spectrometry to structural identification of flavonoid monoglycosides isolated from shoot of lupin (Lupinus luteus L.).
(15/1627)
Flavonoid glycosides constitute important group of plant secondary metabolites. This class of natural products play significant role in different physiological processes. A new methodological approach where mass spectrometric techniques are applied to structural studies of this class of compounds is presented. Four flavonoid O-monoglycosides and one C-monoglycoside were isolated from green parts of lupin (Lupinus luteus L.). Several different mass spectrometric techniques were applied to structural elucidation of isolated compounds. Desorption ionization mass spectrometry was used for registration of mass spectra of intact and derivatized (permethylated) flavonoid glycosides. In some cases electron impact mass spectra of permethylated compounds were also recorded. Methylated samples after methanolysis and further derivatization of free hydroxyl groups (methylation or acetylation) were analyzed with gas chromatography-mass spectrometry. Combined information drawn from the registered mass spectra enabled us to define molecular mass, structure of aglycones and sugars, and positions of glycosidic bonds on the aglycon. Structures of four flavonoid monoglycosides were elucidated as follows: genistein 7-O-glucoside (1), genistein 4'-O-glucoside (2), 2'-hydroxygenistein 7-O-glucoside (3), and apigenin or genistein 8-C-glycoside (5). For the fourth O-glycoside (4) only molecular mass and masses of the aglycone and sugar were estimated. (+info)
AXR1 acts after lateral bud formation to inhibit lateral bud growth in Arabidopsis.
(16/1627)
The AXR1 gene of Arabidopsis is required for many auxin responses. The highly branched shoot phenotype of mature axr1 mutant plants has been taken as genetic evidence for a role of auxin in the control of shoot branching. We compared the development of lateral shoots in wild-type Columbia and axr1-12 plants. In the wild type, the pattern of lateral shoot development depends on the developmental stage of the plant. During prolonged vegetative growth, axillary shoots arise and develop in a basal-apical sequence. After floral transition, axillary shoots arise rapidly along the primary shoot axis and grow out to form lateral inflorescences in an apical-basal sequence. For both patterns, the axr1 mutation does not affect the timing of axillary meristem formation; however, subsequent lateral shoot development proceeds more rapidly in axr1 plants. The outgrowth of lateral inflorescences from excised cauline nodes of wild-type plants is inhibited by apical auxin. axr1-12 nodes are resistant to this inhibition. These results provide evidence for common control of axillary growth in both patterns, and suggest a role for auxin during the late stages of axillary shoot development following the formation of the axillary bud and several axillary leaf primordia. (+info)