Identification and Characterization of a Biodegradative Form of Threonine Dehydratase in Senescing Tomato (Lycopersicon esculentum) Leaf

Szamosi, Iwona T.; Shaner, Dale L.; Singh, Bijay

doi:10.1104/pp.101.3.999

Cited by 30 publications

(13 citation statements)

References 12 publications

(12 reference statements)

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“…Induction of TD2 expression by diverse types of biotic and abiotic stress (Hildmann et al, 1992;Zhao et al, 2003) raises the possibility that the enzyme performs other physiological roles in planta. For example, it is possible that a proteolytically processed form of TD2 accounts for the biodegrative TD activity observed in senescing tomato leaves (Szamosi et al, 1993).…”

Section: Discussion Functional Diversification Of Two Td Isoforms In mentioning

confidence: 99%

Stability of Plant Defense Proteins in the Gut of Insect Herbivores

et al. 2007

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Plant defense against insect herbivores is mediated in part by enzymes that impair digestive processes in the insect gut. Little is known about the evolutionary origins of these enzymes, their distribution in the plant kingdom, or the mechanisms by which they act in the protease-rich environment of the animal digestive tract. One example of such an enzyme is threonine (Thr) deaminase (TD), which in tomato (Solanum lycopersicum) serves a dual role in isoleucine (Ile) biosynthesis in planta and Thr degradation in the insect midgut. Here, we report that tomato uses different TD isozymes to perform these functions. Whereas the constitutively expressed TD1 has a housekeeping role in Ile biosynthesis, expression of TD2 in leaves is activated by the jasmonate signaling pathway in response to herbivore attack. Ingestion of tomato foliage by specialist (Manduca sexta) and generalist (Trichoplusia ni) insect herbivores triggered proteolytic removal of TD2's C-terminal regulatory domain, resulting in an enzyme that degrades Thr without being inhibited through feedback by Ile. This processed form (pTD2) of TD2 accumulated to high levels in the insect midgut and feces (frass). Purified pTD2 exhibited biochemical properties that are consistent with a postingestive role in defense. Shotgun proteomic analysis of frass from tomato-reared M. sexta identified pTD2 as one of the most abundant proteins in the excrement. Among the other tomato proteins identified were several jasmonate-inducible proteins that have a known or proposed role in anti-insect defense. Subtilisin-like proteases and other pathogenesis-related proteins, as well as proteins of unknown function, were also cataloged. We conclude that proteomic analysis of frass from insect herbivores provides a robust experimental approach to identify hyperstable plant proteins that serve important roles in defense.

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Section: Discussion Functional Diversification Of Two Td Isoforms In mentioning

confidence: 99%

Stability of Plant Defense Proteins in the Gut of Insect Herbivores

et al. 2007

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“…At very late stages of development, in senescing leaves showing . This is quite different from tomato, which contains a biodegradative form of TD that is almost fully resistant to feedback inhibition by Ile at stages earlier than senescence (Szamosi et al, 1993). omrl of GMllb must be a mutant allele that encodes an Ileinsensitive, biosynthetic form of TD, since this form appears at germination and continues to be expressed in the plant until senescence (Fig.…”

Section: Co-segregation Of Growth and Enzyme Resistancementioning

confidence: 98%

L-O-Methylthreonine-Resistant Mutant of Arabidopsis Defective in Isoleucine Feedback Regulation

Mourad

King

1995

Plant Physiol.

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Threonine dehydratase/deaminase (TD), the first enzyme in the isoleucine biosynthetic pathway, is feedback inhibited by isoleucine. By screening M, populations of ethyl methane sulfonatetreated Arabidopsis thaliana Columbia wild-type seeds, we isolated five independent mutants that were resistant to i-O-methylthreonine, an isoleucine structural analog. Crowth in the mutants was 50-to 600-fold more resistant to i-Omethylthreonine than in the wild type. l h e resistance was dueto a single, dominant nuclear gene that was denoted omrl and was mapped to chromosome 3 in CM11 b, the mutant line exhibiting the highest level of resistance. Biochemical characteristics (specific activities, K, , V,,,, and pH optimum) of TD in extracts from the wild type and C M l l b were similar except for the inhibition constant of isoleucine, which was 50-fold higher in C M l l b than in the wild type. Levels of free isoleucine were 20-fold higher in extracts from C M l l b than in extracts from wild type. Therefore, isoleucine feedback insensitivity in G M l l b is due to a mutant form of the TD enzyme encoded by omrl. l h e mutant allele Omrl of the line C M l l b could provide a new selectable marker for plant genetic transformation.TD, the first enzyme in the biosynthetic pathway of Ile, catalyzes the formation of 2-oxobutyrate from Thr in a two-step reaction. The first step is a dehydration of Thr followed by rehydration and liberation of ammonia (Bryan, 1990). AI1 the reactions downstream from TD are catalyzed by enzymes that are shared by the two main branches of the biosynthetic pathway that lead to the production of the branched-chain amino acids Ile, Leu, and Val. In bacteria and yeast, resistance to the Ile structural analog thiaIle was associated with a loss of feedback sensitivity of TD to Ile (Umbarger, 1971;Kielland-Brandt et al., 1979). In Rosa cells, resistance to the Ile structural analog OMT was also associated with a TD that had reduced sensitivity to feedback inhibition by Ile (Strauss et al., 1985). Being in tissue culture and having high ploidy level, it was not possible to determine the genetic basis of feedback insensitivity to Ile in the Rasa variant, the only plant mutant with an Ile-insensitive TD.We are isolating and characterizing mutants of the branched-chain amino acid biosynthetic pathway at the ' This work was supported by research grants from the Natural MATERIALS A N D METHODS Seed MutagenesisAbout 100,000 seeds of Arabidopsis tkaliana (L.) Heynh Columbia wild type were allowed to imbibe (v/v) in an aqueous solution of 0.2% EMS for 18 h at room temperature. The mutagenized seed (M,) was washed severa1 times with distilled water, planted in subpopulations, and allowed to self-fertilize to produce M, seed. The M, seed were harvested from each subpopulation separately, surface sterilized, and planted on agar-solidified medium containing 0.5 mM OMT. In this medium wild-type seedlings were completely bleached and died immediately after germination, whereas resistant mutants were able to germinate and prod...

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“…There is ample evidence for the last inference. First, like the biosynthetic Thr dehydratases of microorganisms, plant Thr dehydratases prefer Thr but act also on Ser in vitro (Figures 3B and 3C; Szamosi et al, 1993). Second, levels of Ser are at least equal to those of Thr in both green and non-green plastids and can be far higher (Farré et al, 2001;Szecowka et al, 2013), so that Ser should be abundantly available as a substrate for Thr dehydratase in organello.…”

Section: Rida Preempts Damage From 2-iminopropanoate a Side-product mentioning

confidence: 99%

Arabidopsis and Maize RidA Proteins Preempt Reactive Enamine/Imine Damage to Branched-Chain Amino Acid Biosynthesis in Plastids

et al. 2014

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RidA (for Reactive Intermediate Deaminase A) proteins are ubiquitous, yet their function in eukaryotes is unclear. It is known that deleting Salmonella enterica ridA causes Ser sensitivity and that S. enterica RidA and its homologs from other organisms hydrolyze the enamine/imine intermediates that Thr dehydratase forms from Ser or Thr. In S. enterica, the Ser-derived enamine/imine inactivates a branched-chain aminotransferase; RidA prevents this damage. Arabidopsis thaliana and maize (Zea mays) have a RidA homolog that is predicted to be plastidial. Expression of either homolog complemented the Ser sensitivity of the S. enterica ridA mutant. The purified proteins hydrolyzed the enamines/imines formed by Thr dehydratase from Ser or Thr and protected the Arabidopsis plastidial branched-chain aminotransferase BCAT3 from inactivation by the Ser-derived enamine/imine. In vitro chloroplast import assays and in vivo localization of green fluorescent protein fusions showed that Arabidopsis RidA and Thr dehydratase are chloroplast targeted. Disrupting Arabidopsis RidA reduced root growth and raised the root and shoot levels of the branched-chain amino acid biosynthesis intermediate 2-oxobutanoate; Ser treatment exacerbated these effects in roots. Supplying Ile reversed the root growth defect. These results indicate that plastidial RidA proteins can preempt damage to BCAT3 and Ile biosynthesis by hydrolyzing the Ser-derived enamine/imine product of Thr dehydratase.

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Identification and Characterization of a Biodegradative Form of Threonine Dehydratase in Senescing Tomato (Lycopersicon esculentum) Leaf

Cited by 30 publications

References 12 publications

Stability of Plant Defense Proteins in the Gut of Insect Herbivores

Stability of Plant Defense Proteins in the Gut of Insect Herbivores

L-O-Methylthreonine-Resistant Mutant of Arabidopsis Defective in Isoleucine Feedback Regulation

Arabidopsis and Maize RidA Proteins Preempt Reactive Enamine/Imine Damage to Branched-Chain Amino Acid Biosynthesis in Plastids

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