Iodothyronine deiodinases catalyze the conversion of the thyroid prohormone T 4 to T 3 by outer r... more Iodothyronine deiodinases catalyze the conversion of the thyroid prohormone T 4 to T 3 by outer ring deiodination (ORD) of the iodothyronine molecule. The catalytic cycle of deiodinases is considered to be critically dependent on a reducing thiol cosubstrate that regenerates the selenoenzyme to its native state. The endogenous cosubstrate has still not been firmly identified; in studies in vitro the sulfhydryl reagent dithiothreitol (DTT) is commonly used to activate ORD. We now have characterized an ORD activity in the teleost gilthead seabream (Sparus auratus) that is inhibited by DTT. DTT inhibited reverse T 3 (rT 3) ORD by 70 and 100 % in kidney homogenates (IC 50 0.4 mmol/liter) and microsomes (IC 50 0.1 mmol/liter), respectively. The omission of DTT from the incubation medium restored renal ORD Michaelis-Menten kinetics with a Michaelis constant value of 5 �mol/liter rT 3 and THE CONVERSION, by outer ring deiodination (ORD), of the thyroid hormone T4 to the potent and biologic...
Cysteine-rich receptor-like kinases (CRKs) are transmembrane proteins characterized by
the presen... more Cysteine-rich receptor-like kinases (CRKs) are transmembrane proteins characterized by the presence of two domains of unknown function 26 (DUF26) in their ectodomain. The CRKs form one of the largest groups of receptor-like protein kinases in plants, but their bio- logical functions have so far remained largely uncharacterized. We conducted a large-scale phenotyping approach of a nearly complete crk T-DNA insertion line collection showing that CRKs control important aspects of plant development and stress adaptation in response to biotic and abiotic stimuli in a non-redundant fashion. In particular, the analysis of reactive oxygen species (ROS)-related stress responses, such as regulation of the stomatal aper- ture, suggests that CRKs participate in ROS/redox signalling and sensing. CRKs play gen- eral and fine-tuning roles in the regulation of stomatal closure induced by microbial and abiotic cues. Despite their great number and high similarity, large-scale phenotyping identi- fied specific functions in diverse processes for many CRKs and indicated that CRK2 and CRK5 play predominant roles in growth regulation and stress adaptation, respectively. As a whole, the CRKs contribute to specificity in ROS signalling. Individual CRKs control distinct responses in an antagonistic fashion suggesting future potential for using CRKs in genetic approaches to improve plant performance and stress tolerance.
Plasma membrane-resident receptor kinases (RKs) initiate signaling pathways important for plant i... more Plasma membrane-resident receptor kinases (RKs) initiate signaling pathways important for plant immunity and development. In Arabidopsis (Arabidopsis thaliana), the receptor for the elicitor-active peptide epitope of bacterial flagellin, flg22, is encoded by FLAGELLIN SENSING2 (FLS2), which promotes plant immunity. Despite its relevance, the molecular components regulating FLS2-mediated signaling remain largely unknown. We show that plasma membrane ARABIDOPSIS-AUTOINHIBITED Ca(2+)-ATPase (ACA8) forms a complex with FLS2 in planta. ACA8 and its closest homolog ACA10 are required for limiting the growth of virulent bacteria. One of the earliest flg22 responses is the transient increase of cytosolic Ca(2+) ions, which is crucial for many of the well-described downstream responses (e.g. generation of reactive oxygen species and the transcriptional activation of defense-associated genes). Mutant aca8 aca10 plants show decreased flg22-induced Ca(2+) and reactive oxygen species bursts and ...
Although the hormones, gibberellin and auxin, are known to play a role in the initiation of fruit... more Although the hormones, gibberellin and auxin, are known to play a role in the initiation of fruits, no such function has yet been demonstrated for abscisic acid (ABA). However, ABA signaling and ABA responses are high in tomato (Solanum lycopersicum L.) ovaries before pollination and decrease thereafter (Vriezen et al. in New Phytol 177:60-76, 2008). As a first step to understanding the role of ABA in ovary development and fruit set in tomato, we analyzed ABA content and the expression of genes involved in its metabolism in relation to pollination. We show that ABA levels are relatively high in mature ovaries and decrease directly after pollination, while an increase in the ABA metabolite dihydrophaseic acid was measured. An important regulator of ABA biosynthesis in tomato is 9-cis-epoxy-carotenoid dioxygenase (LeNCED1), whose mRNA level in ovaries is reduced after pollination. The increased catabolism is likely caused by strong induction of one of four newly identified putative (+)ABA 8'-hydroxylase genes. This gene was named SlCYP707A1 and is expressed specifically in ovules and placenta. Transgenic plants, overexpressing SlCYP707A1, have reduced ABA levels and exhibit ABA-deficient phenotypes suggesting that this gene encodes a functional ABA 8'-hydroxylase. Gibberellin and auxin application have different effects on the LeNCED1 and SlCYP707A1 gene expression. The crosstalk between auxins, gibberellins and ABA during fruit set is discussed.
One of the largest groups of recept or-like protein kinases (RLKs) are the CYSTEINE-RICH RLKs (CR... more One of the largest groups of recept or-like protein kinases (RLKs) are the CYSTEINE-RICH RLKs (CRKs) with 44 members in Arabidopsis. CRK expression is regulated in response to variou s stresses that lead to specific alter- ations in ROS metabolism (Wrzaczek et al., 2010). CRKs are characterized by conserved cy steine motifs in the ecto- domain potentially involved in ROS si gnaling. To address this, we have ch aracterized a mutant collection of the Ara- bidopsis CRK family in response to repres entative stresses that are closely link ed to altered ROS production in apo- plast, chloroplasts, mitochondria, and pe roxisomes. In spite of their high level of conservation, phenotypical and in si- lico analysis of the crk mutants revealed specific deregulation of proc esses such as cell death in response to ozone, excess light or UV-B stress, stomatal closure, pathogen susceptibility, plant development, hormone signaling, seed germination, and photosynthetic proce sses. Altogether, our res...
Iodothyronine deiodinases catalyze the conversion of the thyroid prohormone T 4 to T 3 by outer r... more Iodothyronine deiodinases catalyze the conversion of the thyroid prohormone T 4 to T 3 by outer ring deiodination (ORD) of the iodothyronine molecule. The catalytic cycle of deiodinases is considered to be critically dependent on a reducing thiol cosubstrate that regenerates the selenoenzyme to its native state. The endogenous cosubstrate has still not been firmly identified; in studies in vitro the sulfhydryl reagent dithiothreitol (DTT) is commonly used to activate ORD. We now have characterized an ORD activity in the teleost gilthead seabream (Sparus auratus) that is inhibited by DTT. DTT inhibited reverse T 3 (rT 3) ORD by 70 and 100 % in kidney homogenates (IC 50 0.4 mmol/liter) and microsomes (IC 50 0.1 mmol/liter), respectively. The omission of DTT from the incubation medium restored renal ORD Michaelis-Menten kinetics with a Michaelis constant value of 5 �mol/liter rT 3 and THE CONVERSION, by outer ring deiodination (ORD), of the thyroid hormone T4 to the potent and biologic...
Cysteine-rich receptor-like kinases (CRKs) are transmembrane proteins characterized by
the presen... more Cysteine-rich receptor-like kinases (CRKs) are transmembrane proteins characterized by the presence of two domains of unknown function 26 (DUF26) in their ectodomain. The CRKs form one of the largest groups of receptor-like protein kinases in plants, but their bio- logical functions have so far remained largely uncharacterized. We conducted a large-scale phenotyping approach of a nearly complete crk T-DNA insertion line collection showing that CRKs control important aspects of plant development and stress adaptation in response to biotic and abiotic stimuli in a non-redundant fashion. In particular, the analysis of reactive oxygen species (ROS)-related stress responses, such as regulation of the stomatal aper- ture, suggests that CRKs participate in ROS/redox signalling and sensing. CRKs play gen- eral and fine-tuning roles in the regulation of stomatal closure induced by microbial and abiotic cues. Despite their great number and high similarity, large-scale phenotyping identi- fied specific functions in diverse processes for many CRKs and indicated that CRK2 and CRK5 play predominant roles in growth regulation and stress adaptation, respectively. As a whole, the CRKs contribute to specificity in ROS signalling. Individual CRKs control distinct responses in an antagonistic fashion suggesting future potential for using CRKs in genetic approaches to improve plant performance and stress tolerance.
Plasma membrane-resident receptor kinases (RKs) initiate signaling pathways important for plant i... more Plasma membrane-resident receptor kinases (RKs) initiate signaling pathways important for plant immunity and development. In Arabidopsis (Arabidopsis thaliana), the receptor for the elicitor-active peptide epitope of bacterial flagellin, flg22, is encoded by FLAGELLIN SENSING2 (FLS2), which promotes plant immunity. Despite its relevance, the molecular components regulating FLS2-mediated signaling remain largely unknown. We show that plasma membrane ARABIDOPSIS-AUTOINHIBITED Ca(2+)-ATPase (ACA8) forms a complex with FLS2 in planta. ACA8 and its closest homolog ACA10 are required for limiting the growth of virulent bacteria. One of the earliest flg22 responses is the transient increase of cytosolic Ca(2+) ions, which is crucial for many of the well-described downstream responses (e.g. generation of reactive oxygen species and the transcriptional activation of defense-associated genes). Mutant aca8 aca10 plants show decreased flg22-induced Ca(2+) and reactive oxygen species bursts and ...
Although the hormones, gibberellin and auxin, are known to play a role in the initiation of fruit... more Although the hormones, gibberellin and auxin, are known to play a role in the initiation of fruits, no such function has yet been demonstrated for abscisic acid (ABA). However, ABA signaling and ABA responses are high in tomato (Solanum lycopersicum L.) ovaries before pollination and decrease thereafter (Vriezen et al. in New Phytol 177:60-76, 2008). As a first step to understanding the role of ABA in ovary development and fruit set in tomato, we analyzed ABA content and the expression of genes involved in its metabolism in relation to pollination. We show that ABA levels are relatively high in mature ovaries and decrease directly after pollination, while an increase in the ABA metabolite dihydrophaseic acid was measured. An important regulator of ABA biosynthesis in tomato is 9-cis-epoxy-carotenoid dioxygenase (LeNCED1), whose mRNA level in ovaries is reduced after pollination. The increased catabolism is likely caused by strong induction of one of four newly identified putative (+)ABA 8'-hydroxylase genes. This gene was named SlCYP707A1 and is expressed specifically in ovules and placenta. Transgenic plants, overexpressing SlCYP707A1, have reduced ABA levels and exhibit ABA-deficient phenotypes suggesting that this gene encodes a functional ABA 8'-hydroxylase. Gibberellin and auxin application have different effects on the LeNCED1 and SlCYP707A1 gene expression. The crosstalk between auxins, gibberellins and ABA during fruit set is discussed.
One of the largest groups of recept or-like protein kinases (RLKs) are the CYSTEINE-RICH RLKs (CR... more One of the largest groups of recept or-like protein kinases (RLKs) are the CYSTEINE-RICH RLKs (CRKs) with 44 members in Arabidopsis. CRK expression is regulated in response to variou s stresses that lead to specific alter- ations in ROS metabolism (Wrzaczek et al., 2010). CRKs are characterized by conserved cy steine motifs in the ecto- domain potentially involved in ROS si gnaling. To address this, we have ch aracterized a mutant collection of the Ara- bidopsis CRK family in response to repres entative stresses that are closely link ed to altered ROS production in apo- plast, chloroplasts, mitochondria, and pe roxisomes. In spite of their high level of conservation, phenotypical and in si- lico analysis of the crk mutants revealed specific deregulation of proc esses such as cell death in response to ozone, excess light or UV-B stress, stomatal closure, pathogen susceptibility, plant development, hormone signaling, seed germination, and photosynthetic proce sses. Altogether, our res...
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Papers by Lisette Nitsch
the presence of two domains of unknown function 26 (DUF26) in their ectodomain. The
CRKs form one of the largest groups of receptor-like protein kinases in plants, but their bio-
logical functions have so far remained largely uncharacterized. We conducted a large-scale
phenotyping approach of a nearly complete
crk
T-DNA insertion line collection showing that
CRKs control important aspects of plant development and stress adaptation in response to
biotic and abiotic stimuli in a non-redundant fashion. In particular, the analysis of reactive oxygen species (ROS)-related stress responses, such as regulation of the stomatal aper-
ture, suggests that CRKs participate in ROS/redox signalling and sensing. CRKs play gen-
eral and fine-tuning roles in the regulation of stomatal closure induced by microbial and
abiotic cues. Despite their great number and high similarity, large-scale phenotyping identi-
fied specific functions in diverse processes for many CRKs and indicated that CRK2 and
CRK5 play predominant roles in growth regulation and stress adaptation, respectively. As a
whole, the CRKs contribute to specificity in ROS signalling. Individual CRKs control distinct
responses in an antagonistic fashion suggesting future potential for using CRKs in genetic
approaches to improve plant performance and stress tolerance.
the presence of two domains of unknown function 26 (DUF26) in their ectodomain. The
CRKs form one of the largest groups of receptor-like protein kinases in plants, but their bio-
logical functions have so far remained largely uncharacterized. We conducted a large-scale
phenotyping approach of a nearly complete
crk
T-DNA insertion line collection showing that
CRKs control important aspects of plant development and stress adaptation in response to
biotic and abiotic stimuli in a non-redundant fashion. In particular, the analysis of reactive oxygen species (ROS)-related stress responses, such as regulation of the stomatal aper-
ture, suggests that CRKs participate in ROS/redox signalling and sensing. CRKs play gen-
eral and fine-tuning roles in the regulation of stomatal closure induced by microbial and
abiotic cues. Despite their great number and high similarity, large-scale phenotyping identi-
fied specific functions in diverse processes for many CRKs and indicated that CRK2 and
CRK5 play predominant roles in growth regulation and stress adaptation, respectively. As a
whole, the CRKs contribute to specificity in ROS signalling. Individual CRKs control distinct
responses in an antagonistic fashion suggesting future potential for using CRKs in genetic
approaches to improve plant performance and stress tolerance.