A Nicotiana plumbaginifolia protein labeled with an azido cytokinin agonist is a glutathione S‐transferase

Abstract

The mechanisms of reception/transduction of cytokinins still remain largely unknown. We used 1‐(2‐azido‐6‐chloropyrid‐4‐yl)‐3‐(4‐[3H])phenylurea ([3H]azido‐CPPU), a new photoaffinity probe to search for cytokinin‐binding proteins. A soluble protein that binds phenylurea‐type cytokinins has been specifically photolabeled in Nicotiana plumbaginifolia (cv. Viviani line pbH1D) leaf extracts. The protein was purified to homogeneity by affinity chromatography. Its N‐terminal amino acid sequence, as well as four internal peptidic sequences are highly homologous with the theta class of the glutathione S‐transferase superfamily (GST, EC 2.5.1.18) including Hyoscyamus muticus and Arabidopsis GSTs identified as auxin‐binding proteins. The purified N. plumbaginifolia protein also possesses GST enzymatic activity. To test the possible involvement of this GST in the mechanism of action of cytokinin, we studied the binding of tritiated‐CPPU to the purified GST in the presence of various compounds, cytokinin agonists, cytokinin antagonists, or inactive molecules. Thidiazuron is a poor competitor, and neither zeatin nor the active optical isomer R‐MeBA is able to inhibit the binding of CPPU. There is no correlation between the cytokinin activity and the binding properties of the molecules tested. Our results confirmed that plant GSTs bind different compounds, especially plant hormones but probably have no specific role in the mode of action of cytokinins.

A GlutathioneS-Transferase Regulated by Light and Hormones Participates in the Modulation of Arabidopsis Seedling Development

“…Plant GSTs are involved in a number of biotic and abiotic responses, which might be related to GSTs being able to conjugate GSH to different targets, including phytohormones, that regulate various aspects of plant development and thus may affect homeostasis of phytohormones such as auxin (Zettl et al, 1994) or cytokinin (Gonneau et al, 1998) and GSH within the cells or tissues. Changes in GSH levels have been implicated as affecting plant flowering (Ogawa et al, 2001), root elongation (Vernoux et al, 2000;Espunya et al, 2006), chloroplast transcription (Baena-González et al, 2001), and responses to pathogen infection (Gullner et al, 1999).…”

“…They have been shown to bind hormones such as auxin and cytokinin (Zettl et al, 1994;Gonneau et al, 1998) and can be induced by a wide variety of phytohormones, including ethylene, auxin, methyl jasmonate, salicylic acid, and abscisic acid (ABA; Wagner et al, 2002;Moons, 2003;Smith et al, 2003). That all these hormones regulate many aspects of plant development implies that plant GSTs may play vital roles in plant growth and development as well.…”

Crosstalk and differential response to abiotic and biotic stressors reflected at the transcriptional level of effector genes from secondary metabolism

“…Phi and tau GSTs catalyze the glutathionetagging of secondary metabolites including phytoalexins and isothiocyanates, function as glutathione peroxidases or they have non-catalytic roles Dixon et al, 2002). Some GSTs appear to have roles as hormone-or flavonol-binding proteins (Marrs, 1996;Gonneau et al 1998;Smith et al, 2003), as components of UVinducible cell signaling pathways (Loyall et al, 2000) or as potential regulators of apoptosis (Kampranis et al, 2000; for review: Dixon et al, 2002). Zeta GSTs catalyze an important glutathione-dependent isomerization step in the catabolism of tyrosine .…”

Regeneração de plantas de Phaseolus vulgaris L. a partir de calos e transformação genética via Agrobacterium.

“…Apesar de sua grande importância, quase nada é conhecido a respeito do mecanismo de ação ao nível molecular. As citocininas podem ser classificadas em dois grupos: citocininas -adeninas e citocininas -feniluréias (Takahashi et al, 1978;Mok et al, 1982;Gonneau et al, 1998).…”

“…Em estudos da regulação do metabolismo observou-se que o CPPU, assim como outras citocininas, retardam a biossíntese do ácido abscísico (ABA) (Cowan et al, 1999). O mecanismo pelo qual as feniluréias respondem de maneira equivalente as citocininas do grupo das adeninas permanece pouco conhecido, assim como os mecanismos de recepção/transdução das demais citocininas (Gonneau et al, 1998 Entretanto isso resulta em uma baixa eficiência do protocolo de regeneração (Mariotti et al, 1989;Mcclean & Grafton, 1989;Franklin et al, 1991;Mohamed et al, 1992a;Mohamed et al, 1993b;Dillen et al, 1997;Zambre et al, 1998;Zambre et al, 2001 O etileno apresenta vários efeitos morfogenéticos no desenvolvimento das plantas. Pode promover a formação de raízes adventícias e também mediar o efeito de fatores de enraizamento como as auxinas (Bleecker & Kende, 2000).…”