ISSN:1040-4651    

DOI:10.1105/tpc.8.6.939

出版商:American Society of Plant Biologists    

年代:1996

数据来源: ASPB

摘要:

In self-incompatible (SI) plants, the S locus acts to prevent growth of self-pollen and thus promotes outcrossing within the species. Interspecific crosses between SI and self-compatible (SC) species often show unilateral incompatibility that follows the SI x SC rule: SI species reject pollen from SC species, but the reciprocal crosses are usually compatible. The general validity of the SI x SC rule suggests a link between SI and interspecific pollen rejection; however, this link has been questioned because of a number of exceptions to the rule. To clarify the role of the S locus in interspecific pollen rejection, we transformed several Nicotiana species and hybrids with genes encoding SA2 or SC10 RNase from SI N. alata. Compatibility phenotypes in the transgenic plants were tested using pollen from three SC species showing unilateral incompatibility with N. alata. S RNase was implicated in rejecting pollen from all three species. Rejection of N. plumbaginifolia pollen was similar to S allele-specific pollen rejection, showing a requirement for both S RNase and other genetic factors from N. alata. In contrast, S RNase-dependent rejection of N. glutinosa and N. tabacum pollen proceeded without these additional factors. N. alata also rejects pollen from the latter two species through an S RNase-independent mechanism. Our results implicate the S locus in all three systems, but it is clear that multiple mechanisms contribute to interspecific pollen rejection.

ISSN:1040-4651    

DOI:10.1105/tpc.8.6.943

出版商:American Society of Plant Biologists    

年代:1996

数据来源: ASPB

摘要:

To transposon tag the tomato Dwarf (D) gene, a tomato line that carries a T-DNA containing a maize Activator (Ac) transposable element closely linked to D was pollinated with a stock homozygous for the d mutation. Hybrid seedlings were screened for dwarf progeny, and three independent dwarf lines were obtained. Two of these lines showed inheritance of a recessive phenotype similar to that conferred by the extreme dwarf (dx) allele. Variegation for the dwarf phenotype in one of these lines suggested that D had been tagged by Ac. Genomic DNA adjacent to Ac in these two lines was isolated by use of the inverse polymerase chain reaction, and the two insertions mapped approximately 2 kb apart. Partial complementation of d was observed when the corresponding wild-type sequence was used in transformation experiments. A cDNA clone of D was sequenced, and the predicted amino acid sequence has homology to cytochrome P450 enzymes.

ISSN:1040-4651    

出版商:American Society of Plant Biologists    

年代:1996

数据来源: ASPB

摘要:

Collective evidence demonstrates that the Miniature1 (Mn1) seed locus in maize encodes an endosperm-specific isozyme of cell wall Invertase, CWI-2. The evidence includes (1) isolation and characterization of ethyl methanesulfonate-induced mn1 mutants with altered enzyme activity and (2) a near-linear relationship between gene/dose and invertase activity and the CWI-2 protein. In addition, molecular analyses showed that the cDNA clone incw2 maps to the Mn1 locus and differentiates the six ethyl methanesulfonate-induced mn1 mutants of independent origin into two classes when RNA gel blot analyses were used. We also report two unexpected observations that provide significant new insight into the physiological role of invertase and its regulation in a developing seed. First, a large proportion of total enzyme activity (~90%) was dispensable (i.e., nonlimiting). However, below the threshold level of ~6% of wild-type activity, the endosperm enzyme controlled both the sink strength of the developing endosperm as well as the developmental stability of maternal cells in the pedicel in a rate-limiting manner. Our data also suggest an unusually tight coordinate control between the cell wall-bound and the soluble forms of invertase, which are most likely encoded by two separate genes, presumably through metabolic controls mediated by the sugars.

ISSN:1040-4651    

DOI:10.1105/tpc.8.6.971

出版商:American Society of Plant Biologists    

年代:1996

数据来源: ASPB

摘要:

The rice blast fungus expresses a pathogenicity gene, MPG1, during appressorium formation, disease symptom development, and conidiation. The MPG1 gene sequence predicts a small protein belonging to a family of fungal proteins designated hydrophobins. Using random ascospore analysis and genetic complementation, we showed that MPG1 is necessary for infection-related development of Magnaporthe grisea on rice leaves and for full pathogenicity toward susceptible rice cultivars. The protein product of MPG1 appears to interact with hydrophobic surfaces, where it may act as a developmental sensor for appressorium formation. Ultrastructural studies revealed that MPG1 directs formation of a rodlet layer on conidia composed of interwoven ~5-nm rodlets, which contributes to their surface hydrophobicity. Using combined genetic and biochemical approaches, we identified a 15-kD secreted protein with characteristics that establish it as a class I hydrophobin. The protein is able to form detergent-insoluble high molecular mass complexes, is soluble in trifluoroacetic acid, and exhibits mobility shifts after treatment with performic acid. The production of this protein is directed by MPG1.

ISSN:1040-4651    

DOI:10.1105/tpc.8.6.985

出版商:American Society of Plant Biologists    

年代:1996

数据来源: ASPB

摘要:

Antifungal class I [beta]-1,3-glucanases are believed to be part of the constitutive and induced defenses of plants against fungal infection. Unexpectedly, mutants deficient in these enzymes generated by antisense transformation showed markedly reduced lesion size, lesion number, and virus yield in the local-lesion response of Havana 425 tobacco to tobacco mosaic virus (TMV) and of Nicotiana sylvestris to tobacco necrosis virus. These mutants also showed decreased severity of mosaic disease symptoms, delayed spread of symptoms, and reduced yield of virus in the susceptible response of N. sylvestris to TMV. The symptoms of disease in the responses of both plant species were positively correlated with [beta]-1,3-glucanase content in a series of independent transformants. Taken together, these results provide direct evidence that [beta]-1,3-glucanases function in viral pathogenesis. Callose, a substrate for [beta]-1,3-glucanase, acts as a physical barrier to the spread of virus. Callose deposition in and surrounding TMV-induced lesions was increased in the [beta]-1,3-glucanase-deficient, local-lesion Havana 425 host, suggesting as a working hypothesis that decreased susceptibility to virus resulted from increased deposition of callose in response to infection. Our results suggest novel means, based on antisense transformation with host genes, for protecting plants against viral infection. These observations also raise the intriguing possibility that viruses can use a defense response of the host against fungal infection[mdash]production of [beta]-1,3-glucanases[mdash]to promote their own replication and spread.

ISSN:1040-4651    

DOI:10.1105/tpc.8.6.1001

出版商:American Society of Plant Biologists    

年代:1996

数据来源: ASPB

摘要:

Flavonoids are a major class of secondary metabolites that serves a multitude of functions in higher plants, including a recently discovered role in male fertility. Surprisingly, Arabidopsis plants deficient in flavonoid biosynthesis appear to be fully fertile. Using RNA gel blot analysis and polymerase chain reaction-based assays, we have shown that a mutation at the 3' splice acceptor site in the Arabidopsis chalcone synthase gene completely disrupts synthesis of the active form of the enzyme. We also confirmed that this enzyme, which catalyzes the first step of flavonoid biosynthesis, is encoded by a single-copy gene. HPLC analysis of whole flowers and stamens was used to show that plants homozygous for the splice site mutation are completely devoid of flavonoids. This work provides compelling evidence that despite the high levels of these compounds in the pollen of most plant species, flavonoids are not universally required for fertility. The role of flavonoids in plant reproduction may therefore offer an example of convergent functional evolution in secondary metabolism.

ISSN:1040-4651    

DOI:10.1105/tpc.8.6.1013

出版商:American Society of Plant Biologists    

年代:1996

数据来源: ASPB

摘要:

In plants, all aminoacyl-tRNA synthetases are nuclearly encoded, despite the fact that their activities are required in the three protein-synthesizing cell compartments (cytosol, mitochondria, and chloroplasts). To investigate targeting of these enzymes, we cloned cDNAs encoding alanyl-tRNA synthetase (AlaRS) and the corresponding nuclear gene, ALATS, from Arabidopsis by using degenerate polymerase chain reaction primers based on highly conserved regions shared between known AlaRSs from other organisms. Analysis of the transcription of the gene showed the presence of two potential translation initiation codons in some ALATS mRNAs. Translation from the upstream AUG would generate an N-terminal extension with features characteristic of mitochondrial targeting peptides. A polyclonal antibody raised against part of the Arabidopsis AlaRS revealed that the Arabidopsis cytosolic and mitochondrial AlaRSs are immunologically similar, suggesting that both isoforms are encoded by the ALATS gene. In vitro experiments confirmed that two polypeptides can be translated from AlATS transcripts, with most ribosomes initiating on the downstream AUG to give the shorter polypeptide corresponding in size to the cytosolic enzyme. The ability of the presequence encoded between the two initiation codons to direct polypeptides to mitochondria was demonstrated by expression of fusion proteins in tobacco protoplasts and in yeast. We conclude that the ALATS gene encodes both the cytosolic and the mitochondrial forms of AlaRS, depending on which of the two AUG codons is used to initiate translation.

ISSN:1040-4651    

DOI:10.1105/tpc.8.6.1027

出版商:American Society of Plant Biologists    

年代:1996

数据来源: ASPB

摘要:

GT-2 is a novel DNA binding protein that interacts with a triplet functionally defined, positively acting GT-box motifs (GT1-bx, GT2-bx, and GT3-bx) in the rice phytochrome A gene (PHYA) promoter. Data from a transient transfection assay used here show that recombinant GT-2 enhanced transcription from both homologous and heterologous GT-box-containing promoters, thereby indicating that this protein can function as a transcriptional activator in vivo. Previously, we have shown that GT-2 contains separate DNA binding determinants in its N- and C-terminal halves, with binding site preferences for the GT3-bx and GT2-bx promoter motifs, respectively. Here, we demonstrate that the minimal DNA binding domains reside within dual 90-amino acid polypeptide segments encompassing duplicated sequences, termed trihelix regions, in each half of the molecule, plus 15 additional immediately adjacent amino acids downstream. These minimal binding domains retained considerable target sequence selectivity for the different GT-box motifs, but this selectivity was enhanced by a separate polypeptide segment farther downstream on the C-terminal side of each trihelix region. Therefore, the data indicate that the twin DNA binding domains of GT-2 each consist of a general GT-box recognition core with intrinsic differential binding activity toward closely related target motifs and a modified sequence conferring higher resolution reciprocal selectivity between these motifs.

ISSN:1040-4651    

DOI:10.1105/tpc.8.6.1041

出版商:American Society of Plant Biologists    

年代:1996

数据来源: ASPB

摘要:

Abscisic acid (ABA) induces a rapid and transient mitogen-activated protein (MAP) kinase activation in barley aleurone protoplasts. MAP kinase activity, measured as myelin basic protein phosphorylation by MAP kinase immunoprecipitates, increased after 1 min, peaked after 3 min, and decreased to basal levels after ~5 min of ABA treatment in vivo. Antibodies recognizing phosphorylated tyrosine residues precipitate with myelin basic protein kinase activity that has identical ABA activation characteristics and demonstrate that tyrosine phosphorylation of MAP kinase occurs during activation. The half-maximal concentration of ABA required for MAP kinase activation, 3 x 10-7 M, is very similar to that required for ABA-induced rab16 gene expression. The tyrosine phosphatase inhibitor phenylarsine oxide can completely block ABA-induced MAP kinase activation and rab16 gene expression. These results lead us to conclude that ABA activates MAP kinase via a tyrosine phosphatase and that these steps are a prerequisite for ABA induction of rab16 gene expression.

ISSN:1040-4651    

DOI:10.1105/tpc.8.6.1061

出版商:American Society of Plant Biologists    

年代:1996

数据来源: ASPB