The extensin multigene family responds differentially to superoxide or hydrogen peroxide in tomato cell cultures.
(49/9588)
Changes in extensin gene expression were examined in cultured tomato cells following treatments leading to the production of activated oxygen species. Digitonin, a steroid glycoalkaloid compound, has been shown to trigger a rapid and transient production of superoxide anion, O2-*. 6 h after application of 50 or 100 microM of digitonin, the accumulation of four extensin transcripts (1.5, 2.6, 4.0 and 6.1 kb) was observed. Superoxide dismutase strongly inhibited the digitonin-mediated response, suggesting a key role of O2-* in the signalling cascade. Furthermore, cells treated with enzymatically produced O2-* generated by xanthine oxidase (0.015 U/ml) gave a similar extensin response and again, SOD exerted a strong inhibitory effect on the response. On the other hand, H2O2 (2 mM) or the enzymatic H2O2 generator, glucose oxidase (0.34 U/ml), elicited the accumulation of only three of the four transcripts (1.5, 2.6 and 4.0 kb), indicating that the corresponding genes could be regulated either by H2O2 or O2-* but that the gene encoding the 6.1 kb transcript was exclusively expressed in response to O2-*. Finally, it was shown that lipid peroxidation, which was only induced when cells were exposed to H2O2, did not participate in the AOS-mediated gene expression for extensin. It can be concluded from these results that tomato cells are able to discriminate H2O2 from O2-* and they probably sense the latter by the specific oxidation of an extracellular component. (+info)
atSRp30, one of two SF2/ASF-like proteins from Arabidopsis thaliana, regulates splicing of specific plant genes.
(50/9588)
SR proteins are nuclear phosphoproteins with a characteristic Ser/Arg-rich domain and one or two RNA recognition motifs. They are highly conserved in animals and plants and play important roles in spliceosome assembly and alternative splicing regulation. We have now isolated and partially sequenced a plant protein, which crossreacts with antibodies to human SR proteins. The sequence of the corresponding cDNA and genomic clones from Arabidopsis revealed a protein, atSRp30, with strong similarity to the human SR protein SF2/ASF and to atSRp34/SR1, a previously identified SR protein, indicating that plants possess two SF2/ASF-like proteins. atSRp30 expresses alternatively spliced mRNA isoforms that are expressed differentially in various organs and during development. Overexpression of atSRp30 via a strong constitutive promoter resulted in changes in alternative splicing of several endogenous plant genes, including atSRp30 itself. Interestingly, atSRp30 overexpression resulted in a pronounced down-regulation of endogenous mRNA encoding full-length atSRp34/SR1 protein. Transgenic plants overexpressing atSRp30 showed morphological and developmental changes affecting mostly developmental phase transitions. atSRp30- and atSRp34/SR1-promoter-GUS constructs exhibited complementary expression patterns during early seedling development and root formation, with overlapping expression in floral tissues. The results of the structural and expression analyses of both genes suggest that atSRp34/SR1 acts as a general splicing factor, whereas atSRp30 functions as a specific splicing modulator. (+info)
Arabidopsis STERILE APETALA, a multifunctional gene regulating inflorescence, flower, and ovule development.
(51/9588)
A recessive mutation in the Arabidopsis STERILE APETALA (SAP) causes severe aberrations in inflorescence and flower and ovule development. In sap flowers, sepals are carpelloid, petals are short and narrow or absent, and anthers are degenerated. Megasporogenesis, the process of meiotic divisions preceding the female gametophyte formation, is arrested in sap ovules during or just after the first meiotic division. More severe aberrations were observed in double mutants between sap and mutant alleles of the floral homeotic gene APETALA2 (AP2) suggesting that both genes are involved in the initiation of female gametophyte development. Together with the organ identity gene AGAMOUS (AG) SAP is required for the maintenance of floral identity acting in a manner similar to APETALA1. In contrast to the outer two floral organs in sap mutant flowers, normal sepals and petals develop in ag/sap double mutants, indicating that SAP negatively regulates AG expression in the perianth whorls. This supposed cadastral function of SAP is supported by in situ hybridization experiments showing ectopic expression of AG in the sap mutant. We have cloned the SAP gene by transposon tagging and revealed that it encodes a novel protein with sequence motifs, that are also present in plant and animal transcription regulators. Consistent with the mutant phenotype, SAP is expressed in inflorescence and floral meristems, floral organ primordia, and ovules. Taken together, we propose that SAP belongs to a new class of transcription regulators essential for a number of processes in Arabidopsis flower development. (+info)
In the Nicotiana sylvestris CMSII mutant, a recombination-mediated change 5' to the first exon of the mitochondrial nad1 gene is associated with lack of the NADH:ubiquinone oxidoreductase (complex I) NAD1 subunit.
(52/9588)
We previously reported that the Nicotiana sylvestris CMSII mutant mitochondrial DNA carried a large deletion. Several expressed sequences, most of which are duplicated, and the unique copy of the nad7 gene encoding the NAD7 subunit of the NADH:ubiquinone oxidoreductase complex (complex I) are found in the deletion. Here, we show that the orf87-nad3-nad1/A cotranscription unit transcribed from a unique promoter element in the wild-type, is disrupted in CMSII. Nad3, orf87 and the promoter element are part of the deleted sequence, whilst the nad1/A sequence is present and transcribed from a new promoter brought by the recombination event, as indicated by Northern and primer extension experiments. However, Western analyses of mitochondrial protein fractions and of complex I purified using anti-NAD9 affinity columns, revealed that NAD1 is lacking in CMSII mitochondria. Our results suggest that translation of nad1 transcripts rather than transcription itself could be altered in the mutant. Consequences of lack of this submit belonging the membrane arm of complex I and thought to contain the ubiquinone-binding site, are discussed. (+info)
Characterization of two chloroplast RNA polymerase sigma factors from Zea mays: photoregulation and differential expression.
(53/9588)
Two distinct cDNAs encoding putative sigma factors of plastid RNA polymerase were isolated from Zea mays, a C4 plant. The deduced amino acid sequences of both cDNAs possess all four highly conserved domains proposed for recognition of -10 and -35 promoter elements, core complex binding, DNA binding, and melting. These two cDNAs are designated sig1 and sig2. Phylogenetic analysis of available plastid sigma factors indicated that they were probably the descendants of cyanobacterial principal sigma factors. Southern blots probed with sig1 and sig2 revealed that both genes exist in the maize nuclear genome as single-copy genes, but low-stringency hybridization suggested the presence of a multigene family of maize plastid sigma factors. Transcription of sig1 and sig2 is light inducible and tissue specific. Transcripts of sig1 and sig2 were abundant in greening leaf tissues; sig2 (but not sig1) was barely detectable in etiolated leaves and neither was detectable in roots. Immunological studies using a peptide antibody against an epitope in subdomain 2.4 of Sig1 revealed 50-kDa and 60-kDa immunoreactive proteins in maize chloroplasts. Reduced levels of the 60-kDa immunoreactive protein were detected in etioplasts, and no immunoreactive proteins were observed in roots. Collectively, the data suggest that the nuclear genes, sig1 and sig2, may play a role in differential expression of plastid genes during chloroplast biogenesis. (+info)
Regulatory interaction of PRL1 WD protein with Arabidopsis SNF1-like protein kinases.
(54/9588)
Mutation of the PRL1 gene, encoding a regulatory WD protein, results in glucose hypersensitivity and derepression of glucose-regulated genes in Arabidopsis. The yeast SNF1 protein kinase, a key regulator of glucose signaling, and Arabidopsis SNF1 homologs AKIN10 and AKIN11, which can complement the Deltasnf1 mutation, were found to interact with an N-terminal domain of the PRL1 protein in the two-hybrid system and in vitro. AKIN10 and AKIN11 suppress the yeast Deltasnf4 mutation and interact with the SNF4p-activating subunit of SNF1. PRL1 and SNF4 bind independently to adjacent C-terminal domains of AKIN10 and AKIN11, and these protein interactions are negatively regulated by glucose in yeast. AKIN10 and AKIN11, purified in fusion with glutathione S-transferase, undergo autophosphorylation and phosphorylate a peptide of sucrose phosphate synthase in vitro. The sucrose phosphate synthase-peptide kinase activity of AKIN complexes detected by immunoprecipitation is stimulated by sucrose in light-grown Arabidopsis plants. In comparison with wild type, the activation level of AKIN immunocomplexes is higher in the prl1 mutant, suggesting that PRL1 is a negative regulator of Arabidopsis SNF1 homologs. This conclusion is supported by the observation that PRL1 is an inhibitor of AKIN10 and AKIN11 in vitro. (+info)
Impacts of seed and pollen flow on population genetic structure for plant genomes with three contrasting modes of inheritance.
(55/9588)
The classical island and one-dimensional stepping-stone models of population genetic structure developed for animal populations are extended to hermaphrodite plant populations to study the behavior of biparentally inherited nuclear genes and organelle genes with paternal and maternal inheritance. By substituting appropriate values for effective population sizes and migration rates of the genes concerned into the classical models, expressions for genetic differentiation and correlation in gene frequency between populations can be derived. For both models, differentiation for maternally inherited genes at migration-drift equilibrium is greater than that for paternally inherited genes, which in turn is greater than that for biparentally inherited nuclear genes. In the stepping-stone model, the change of genetic correlation with distance is influenced by the mode of inheritance of the gene and the relative values of long- and short-distance migration by seed and pollen. In situations where it is possible to measure simultaneously Fst for genes with all three types of inheritance, estimates of the relative rates of pollen to seed flow can be made for both the short- and long-distance components of migration in the stepping-stone model. (+info)
CRABS CLAW and SPATULA, two Arabidopsis genes that control carpel development in parallel with AGAMOUS.
(56/9588)
To help understand the process of carpel morphogenesis, the roles of three carpel development genes have been partitioned genetically. Mutants of CRABS CLAW cause the gynoecium to develop into a wider but shorter structure, and the two carpels are unfused at the apex. Mutants of a second gene, SPATULA, show reduced growth of the style, stigma, and septum, and the transmitting tract is absent. Double mutants of crabs claw and spatula with homeotic mutants that develop ectopic carpels demonstrate that CRABS CLAW and SPATULA are necessary for, and inseparable from, carpel development, and that their action is negatively regulated by A and B organ identity genes. The third carpel gene studied, AGAMOUS, encodes C function that has been proposed to fully specify carpel identity. When AGAMOUS function is removed together with the A class gene APETALA2, however, the organs retain many carpelloid properties, suggesting that other genes are also involved. We show here that further mutant disruption of both CRABS CLAW and SPATULA function removes remaining carpelloid properties, revealing that the three genes together are necessary to generate the mature gynoecium. In particular, AGAMOUS is required to specify the identity of the carpel wall and to promote the stylar outgrowth at the apex, CRABS CLAW suppresses radial growth of the developing gynoecium but promotes its longitudinal growth, and SPATULA supports development of the carpel margins and tissues derived from them. The three genes mostly act independently, although there is genetic evidence that CRABS CLAW enhances AGAMOUS and SPATULA function. (+info)