Three distinct basic 14-kD proteins, P14a, P14b, and P14c, were isolated from tomato (Lycopersicon esculentum Mill. cv Baby) leaves infected with Phytophthora infestans. They exhibited antifungal activity against P. infestam both in vitro (inhibition of zoospore germination) and in vivo with a tomato leaf disc assay (decrease in infected leaf surface). Serological cross-reactions and amino acid sequence comparisons showed that the three proteins are members of the PR-1 group of pathogenesis-related (PR) proteins. P14a and P14b showed high similarity to a previously characterized P14, whereas P14c was found to be very similar to a putative basic-type PR-1 from tobacco predicted from isolated DNA clones. This protein, named PR-1 g, was purified from virus-infected tobacco (Nicotiana tabacum Samsun NN) leaves and characterized by amino acid microsequencing, along with the well-known acidic tobacco PR-la, PR-lb, and PR-lc. l h e various tomato and tobacco PR-1 proteins were compared for their biological activity and found to display differential fungicidal activity against P. infestam in both the in vitro and in vivo assays, the most efficient being the newly characterized tomato P14c and tobacco PR-1 g.

No abstract

In carotenoid-deficient albina mutants of barley and in barley plants treated with the herbicide Norflurdzon the light-dependent accumulation of the mRNA for the light-harvesting chlorophyll a/h protein (LHCP) is blocked. Thus, the elimination of a functional chloroplast, either as a result of mutation or as a result of herbicide treatment, can lead to the specific suppression of the expression of a nuclear gene encoding a plastid-localizcd protein. These results confirm and extend earlier observations on maize Euv. J.Biochem. 144, 79 -841. The inhibition of mRNA accumulation appears to be specific for the LHCP; the mRNAs encoding the small subunit of ribulose-1,5-bisphosphate carboxylase and the NADPH : protochlorophyllide oxidoreductase are relatively unaffected. The failure of the albina mutants and of Norflurazon-treated plants to accumulate the LHCP mRNA is not exclusively caused by an instability of the transcript but rather by the inability of the plants to enhance the rate of transcription of the LHCP genes during illumination. Several chlorophyll-deficient xantha mutants of barley, which are blocked after protoporphyrin IX or Mg-protoporphyrin, and the chlorophyll-h-less mutant chlorina f 2 accumulate the LHCP mRNA to almost normal levels during illumination. Thus, if any of the reactions leading to chlorophyll formation is involved in the control of LHCP mRNA accumulation it should be one between the formation of protochlorophyllide and the esterification of chlorophyllide a.While the nature of the regulatory factor(s) has not been identified our results suggest that, in addition to phytochrome (Pfr), plastid-dependent factors are required for a continuous light-dependent transcription of nuclear genes encoding the LHCP.The light-induced transformation of etioplasts into chloroplasts in higher plants depends on an intimate interaction of the nuclear and plastid genomes [I -31. Many plastidlocalized proteins are nucleus-encoded and synthesized on cytoplasmic 80s ribosomes [4]. Some of these nucleus-encoded proteins form functional complexes with chloroplast-encoded proteins. Polypeptides comprising a given complex generally accumulate in a coordinate fashion. The basis of this apparent coordinate genc expression is unknown.One of the most prominent nucleus-encoded plastid membrane proteins, whose appearance is controlled by light, is the light-harvesting chlorophyll a/h protein (LHCP) [5 -71. While the assembly of the complete chlorophyll protein complex depends on the cooperation of at least two distinct photoreceptors, phytochrome and protochlorophyllide [8, 91, a rapid increase of the mRNA encoding the apoprotein of the LHCP can be induced by phytochrome alone [lo, 111. Similar phytochrome-induced changes in the concentration of specific niRNAs have been found for other nuclear-encoded plastid proteins, namely the small subunit of the ribulose-1,5-bisphosphate carboxylase and the NADPH: protochlorophyllide oxidoreductase 112-171. In all three cases it has been demonstrated that the photoreceptor is ...

The transcriptional rates of four different genes in shoots of barley grown under different light regimes were quantified by monitoring nuclear RNA transcripts using gene-specific hybridization probes. Isolated nuclei were pulse-labelled with [cx-~'P]UTP and the relative rates of light-harvesting chlorophyll a/b protein (LHCP) mRNA, NADPH : protochlorophyllide oxidoreductase mRNA, B1 hordein mRNA, and 26-S rRNA synthesis were measured. Irradiation of dark-grown plants with a red light pulse increased the rate of LHCP mRNA synthesis tenfold within 3 h, and the rate of rRNA synthesis more than twofold within 9 h. The relative rate of synthesis of the oxidoreductase mRNA decreased following a red light pulse reaching a minimum after 3 -6 h. As a direct proof of phytochrome involvement in the light-induced stimulation of LHCP and the repression of the oxidoreductase transcripts for both responses, red/far-red reversibility could be demonstrated. We conclude that phytochrome is able both to increase the transcription of certain nuclear genes and decrease the transcription of others.The light-dependent control of plant development is one of the central themes of current plant biology [I]. Light has been shown to induce an increase in a number of mRNA species encoding, for instance, several plastid-specific proteins like the light-harvesting chlorophyll a/b protein and the small subunit of the ribulose-I ,5-bisphosphate carboxylase [2-131. At the same time the concentration of other transcripts, e.g. those coding for the NADPH : protochlorophyllide oxidoreductase (reductase) and phytochrome, is drastically reduced upon illumination of darkgrown plants [14-171. In both instances the reciprocal effect of light on the level of these two groups of mRNAs is mediated by the same photoreceptor phytochrome [3, 5, 6, 8 -1 1,13 -171. These light effects could occur by two possible mechanisms : a phytochrome-controlled change in the rate of transcription initiation and/or a phytochrome-induced change in the stability of transcripts. In the present study we have concentrated on elucidating the first of these two mechanisms. Isolated nuclei of barley have been pulse-labelled and the newly synthesized transcripts analyzed. Available evidence suggests that the majority of RNA synthesis in isolated nuclei represents elongation of already initiated RNA chains and that the rates of transcription in pulse-labelled isolated nuclei can be monitored accurately without the complications of RNA processing or stabilization which occurs within the intact cell [18]. In previous studies it could be demonstrated [I91 that phytochrome controls the overall transcription rate in isolated Avena nuclei. Studies on the synthesis of specific transcripts in isolated nuclei of pea and duckweed, a lightinduced increase in the rate of transcription of genes encoding the light-harvesting chlorophyll a/b protein and the small subunit of the ribulose-l,5-bisphosphate carboxylase has been described [12, 131. This light effect was mediated by phytochrome [13]. As...

Tomato (Lycopersicon esculentum 1.) plants were sprayed with aqueous solutions of isomers of aminobutyric acid and were either analyzed for the accumulation of pathogenesis-related (PR) proteins or challenged with the late blight fungal agent Phyfophthora infestam. The @ isomer of aminobutyric acid induced the accumulation of high levels of three proteins: P14a, @-1,3 glucanase, and chitinase. These proteins either did not accumulate or accumulated to a much lower leve1 in a-or y-aminobutyric acid-treated plants. Plants pretreated with a-, 8-, and 7-aminobutyric acid were protected up to 11 d to an extent of 35, 92, and 6%, respedively, against a challenge infedion with P. infestans. Protection by @-aminobutyric acid was afforded against the blight even when the chemical was applied 1 d postinoculation. Examination of ethylene evolution showed that a-aminobutyric acid induced the produdion of 3-fold higher levels of ethylene compared with @-aminobutyric acid, whereas y-aminobutyric acid induced no ethylene production. In addition, silver thiosulfate, a potent inhibitor of ethylene adion, did not abolish the resistance induced by @-aminobutyric acid. The results are consistent with the possibility that @-aminobutyric acid protects tomato foliage against the late blight disease by a mechanism that is not mediated by ethylene and that PR proteins can be involved in induced resistance.