The coordinated induced expression of b-oxidation genes is essential to provide the energy supply for germination and postgerminative development. However, very little is known about other functions of b-oxidation in nonreserve organs. We have identified a gene-specific pattern of induced b-oxidation gene expression in wounded leaves of Arabidopsis. Mechanical damage triggered the local and systemic induction of only ACX1 among acyl-coenzyme A oxidase (ACX) genes, and KAT2/ PED1 among 3-ketoacyl-coenzyme A thiolase (KAT) genes in Arabidopsis. In turn, wounding induced KAT5/PKT2 only systemically. Although most of the b-oxidation genes were activated by wound-related factors such as dehydration and abscisic acid, jasmonic acid (JA) induced only ACX1 and KAT5. Reduced expression of ACX1 or KAT2 genes, in transgenic plants expressing their corresponding mRNAs in antisense orientation, correlated with defective wound-activated synthesis of JA and with reduced expression of JA-responsive genes. Induced expression of JA-responsive genes by exogenous application of JA was unaffected in those transgenic plants, suggesting that ACX1 and KAT2 play a major role in driving wound-activated responses by participating in the biosynthesis of JA in wounded Arabidopsis plants.Plants often undergo the onslaught of chewing insects or larger herbivores that cause damage to the leaves. Preexisting physical barriers may not be enough to prevent injuries and thus, plants require active inducible defense mechanisms. Moreover, once an injury occurs there is no possibility of wound healing by mobilization of specialized cells as it occurs in animals. In plants, every cell has become competent for the activation of wound-triggered defense responses. Wound-activated defense relies on the production or release of signals in the damaged tissues and the local and systemic activation of signaling pathways (Leó n et al., 2001). Wound-activated signaling pathways usually lead to the transcriptional activation of defense-related genes. In addition, damaged areas undergo a severe disorder of tissue and cellular structures that is accompanied by a drastic loss of water (Reymond et al., 2000). Wound-activated gene expression seems to be the result of the combined action of damage and water stress of the wounded leaf (Reymond et al., 2000), processes that require the synthesis, accumulation, and perception of jasmonic acid (JA) and abscisic acid (ABA; Peñ a- Cortés et al., 1995; Bergey et al., 1996). The signaling function of jasmonates in wound-activated defense has been extensively documented (Turner et al., 2002). Besides, jasmonates are also involved in pathogen-triggered defense in coordination with the function of salicylic acid (SA; Glazebrook et al., 2003).Plants synthesize jasmonates from linolenic acid through the octadecanoid pathway (Schaller, 2001). This is a complex metabolic pathway involving the participation of different subcellular organelles. The release of linolenic acid from membrane lipids and subsequent redox reactions to 12-oxo...

Recently, we described the ubiquitylation of PYL4 and PYR1 by the RING E3 ubiquitin ligase RSL1 at the plasma membrane of This suggested that ubiquitylated abscisic acid (ABA) receptors might be targeted to the vacuolar degradation pathway because such ubiquitylation is usually an internalization signal for the endocytic route. Here, we show that FYVE1 (previously termed FREE1), a recently described component of the endosomal sorting complex required for transport (ESCRT) machinery, interacted with RSL1-receptor complexes and recruited PYL4 to endosomal compartments. Although the ESCRT pathway has been assumed to be reserved for integral membrane proteins, we show the involvement of this pathway in the degradation of ABA receptors, which can be associated with membranes but are not integral membrane proteins. Knockdown alleles are hypersensitive to ABA, illustrating the biological relevance of the ESCRT pathway for the modulation of ABA signaling. In addition, mutants are impaired in the targeting of ABA receptors for vacuolar degradation, leading to increased accumulation of PYL4 and an enhanced response to ABA Pharmacological and genetic approaches revealed a dynamic turnover of ABA receptors from the plasma membrane to the endosomal/vacuolar degradation pathway, which was mediated by FYVE1 and was dependent on RSL1. This process involves clathrin-mediated endocytosis and trafficking of PYL4 through the ESCRT pathway, which helps to regulate the turnover of ABA receptors and attenuate ABA signaling.

Abscisic acid (ABA) is a phytohormone that inhibits growth and enhances adaptation to stress in plants. ABA perception and signaling rely on its binding to receptors of the pyrabactin resistance1/PYR1-like/regulatory components of ABA receptors (PYR/PYL/RCAR) family, the subsequent inhibition of clade A type 2C protein phosphatases (PP2Cs), and the phosphorylation of ion channels and transcription factors by protein kinases of the SnRK2 family. Nitric oxide (NO) may inhibit ABA signaling because NO-deficient plants are hypersensitive to ABA. Regulation by NO often involves posttranslational modification of proteins. Mass spectrometry analysis of ABA receptors expressed in plants and recombinant receptors modified in vitro revealed that the receptors were nitrated at tyrosine residues and S-nitrosylated at cysteine residues. In an in vitro ABA-induced, PP2C inhibition assay, tyrosine nitration reduced receptor activity, whereas S-nitrosylated receptors were fully capable of ABA-induced inhibition of the phosphatase. PYR/PYL/RCAR proteins with nitrated tyrosine, which is an irreversible covalent modification, were polyubiquitylated and underwent proteasome-mediated degradation. We propose that tyrosine nitration, which requires NO and superoxide anions, is a rapid mechanism by which NO limits ABA signaling under conditions in which NO and reactive oxygen species are both produced.