Alleles of Pto and Fen occur in bacterial speck-susceptible and fenthion-insensitive tomato cultivars and encode active protein kinases.

Abstract

The Pto gene was derived originally from the wíld tomato species Lycopersicon pimpinellifolium and confers resistance to Pseudomonas syringae pv tomato strains expressing the avirulence gene avrPto. The Fen gene is also derived from L. pimpinellifolium and confers sensitivity to the insecticide fenthion. We have now isolated and characterized the alleles of Pto and Fen from cultivated tomato, L. esculentum, and designated them pfo and fen. High conservation of genome organization between the two tomato species allowed us to ídentífy the pto and fen alleles from among the cluster of closely related Pfo gene family members. The pto and fen alleles are transcribed and have uninterrupted open reading frames that code for predicted proteins that are 87 and 98% identical to the Pto and Fen protein kinases, respectively. In vitro autophosphorylation assays revealed that both the pto and fen alleles encode active kinases. In addition, the pto kinase phosphorylates a previously characterized substrate of Pto, the Pto-interacting Ptil serine/ threonine kinase. However, the pto kinase shows impaired interaction with Ptil and with several previously isolated Pto-interacting proteins in the yeast two-hybrid system. The observation that pto and fen are active kinases and yet do not confer bacterial speck resistance or fenthion sensitivity suggests that the amino acid substitutions distinguishing them from Pto and Fen may interfere with recognition of the corresponding signal molecule or with protein-protein interactions involved in the Pto-and fen-mediated signal transduction pathways.

Tissue distribution of cholinesterases and anticholinesterases in native and transgenic tomato plants

“…Whether these new functions of a-tomatine may be related to its anticholinesterase activities is still not known, but this is a tempting speculation. The organophosphate cholinesterase inhibitor fenthion triggers the formation of hypersensitive response-like lesions in susceptible tomato plants harboring mutations in fen, another kinaseencoding member of the pto disease-resistance gene family of tomato (Jia et al, 1997;Oldroyd and Staskawicz, 1998). This suggests the involvement of kinase-induced cascades in the signal transduction processes associated with anticholinesterase activities, similar to the report in mice (Birikh et al, 2003).…”

Isolation of Resistance Gene Candidates (RGCs) and characterization of an RGC cluster in cassava

“…In the Mla gene cluster three families of RGCs were grouped with two families of defense-related genes (Wei et al 2002). In the same manner, five Ser/Thr kinase Pto homologs lie adjacent to the Prf gene that it is necessary to the function of Pto (Jia et al 1997). The presence of transposon-like elements in R-gene clusters provides the capacity to induce new specificities through duplication, inversion and transposition events.…”

Homologous and heterologous desensitization and synergy in pathways leading to the soybean oxidative burst

“…Research from a number of laboratories has shown that many low-molecular-weight compounds, known as elicitors, can inaugurate the oxidative burst in both whole plants and cell cultures (recent reviews include Lamb and Dixon 1997;Wojtaszek 1997;Bolwell 1999). In our investigations of the oxidative burst, we have used such elicitors as oligogalacturonic acid (OGA), a plant cell wall fragment (Legendre et al 1993a), harpin, a heatstable protein from the pathogenic bacterium Erwinia amylovora (Wei et al 1992;Baker et al 1993), fensulfothion, an organophosphorous insecticide that activates a Pto family member (Chandra et al 1996;Jia et al 1997) and mechanical or hypo-osmotic stress (Yahraus et al 1995). Several second messengers in the above signaling pathways have also been identi®ed, the best characterized of which are found in the OGA-initiated signaling cascade.…”