No abstract

PR-10 proteins (pathogensis-related), ubiquitous within the plant kingdom, are usually encoded by multigene families. To date we have identified 10 homologous pr-10 genes in a yellow lupine cDNA library. Here, the structure and expression of two newly identified yellow lupine pr-10 genes (LlYpr10-2b and LlYpr10-2f) are presented. Many potential regulatory sites were found in both gene promoters including common ones as well as those unique for each gene. However, promoter deletion analysis in transgenic tobacco plants revealed similar patterns of reporter gene (gus) expression. Shortened fragments of both gene promoters studied caused high GUS activity in leaves (along vascular bundles), stamen stigma, anthers and pollen grains. When conjugated with longer LlYpr-10.2 promoter fragments, GUS was additionally present in petal edges. Only a long fragment of the LlYpr10-2b gene promoter caused GUS expression in the stem. In yellow lupine the pr-10.2 genes are present in all studied organs, but their level of expression depends on the stage of development and is affected by wounding, oxidative stress and salicylic acid treatment. Silencing of the Llpr-10.2b gene in 4-week-old yellow lupine plants did not lead to any visible symptoms, which suggests that the function of the silenced gene is supplemented by its close homologues, still present in the studied plants.

Phytohormones (plant hormones) play a role in the regulation of cellular activities including cell division, elongation and differentiation, pattern formation, organogenesis, reproduction, sex determination, and responses to abiotic and biotic stress. The phytohormonal signal transduction pathways operate via cytokinin perception by transmembrane receptors consisting of two domains: an extracellular domain responsible for hormone binding and an intracellular domain, sensory His / Asp kinase (HK). Upon phytohormone binding, the receptor undergoes a conformational change which activates its protein kinase activity. The phosphorylated intracellular domain transfers the phosphoryl group to the His residue of the histidine phosphotransfer protein (HPt) which in turn phosphorylates Asp residue in the Response Regulator (RR). The phosphorylated RR protein acts as either a positive or negative transcription factor that interacts with the gene promoter or other target protein. The two-component signaling pathway, operating through the His-Asp phosphorelay, controls many physiological and developmental processes throughout the plant lifecycle (from seed-to-seed). Downstream plant hormone signaling also includes proteolysis of transcriptional regulators that block the activity of transcription factors. Two-component signaling operates more frequently in higher plants. Five classic plant hormones had been discovered by the middle of the twentieth century: auxins, cytokinins, gibberellins, ethylene and abscisic acid. The more recently characterized hormones include brassinosteroids, strigolactones, jasmonates and salicylates. Considering the tremendous work that has been undertaken during the last decades, in this review we decided to concentrate on cytokinin signaling in various plant developmental processes, including responses to biotic and abiotic stresses.