16-Systemic acquired resistance (SAR) prepares infected plants for faster and stronger 17 defense activation upon subsequent attacks. SAR requires an information relay from primary 18 infection to distal tissue and the initiation and maintenance of a self-maintaining 19 phytohormone salicylic acid (SA)-defense loop. 20 -In spatial and temporal resolution we show that calcium-dependent protein kinase CPK5 21 contributes to immunity and SAR. In local basal resistance CPK5 functions upstream of SA-22 synthesis, -perception, and -signaling. In systemic tissue, enhanced CPK5 signaling leads to 23 an accumulation of SAR marker genes including transcription factor Systemic Acquired 24Resistance Deficient 1 (SARD1). 25 -Plants of enhanced CPK5-, but not CPK6-, signaling display a 'super-priming' phenotype of 26 enhanced resistance toward a secondary bacterial infection. In sard1 background, CPK5-27 mediated basal resistance is still mounted but systemic 'super-priming' is lost. 28 -The biochemical analysis determines CPK5 half maximal kinase activity for calcium K50 29[Ca 2+ ] to ~100 nM close to the cytoplasmic resting level. This low activation threshold 30 uniquely qualifies CPK5 to decode subtle changes in calcium prerequisite to immune signal 31 relay and to onset and maintenance of priming at later time points in distal tissue. Our data 32 explain why CPK5 functions as a hub in basal and systemic plant immunity. 33 34

We have isolated and characterised three barley cDNAs encoding glutathione peroxidase (GPX) homologues, designated HVGPH1, HVGPH2 and HVGPH3. HVGPH1 may represent a cytosolic form of GPX. The structure of the HVGPH2 N-terminal domain is typical for a plastid transit peptide. A potential peroxisomal targeting sequence occurs near the N-terminus of HVGPH3. Transcript levels of HVGPH1 and HVGPH2 were increased in leaves undergoing stress. In contrast, HVGPH3 mRNA accumulation showed a negative response to stress. Our data indicate that the barley genome bears a small gene family encoding GPX homologues differing in their function and cellular localisation.z 1999 Federation of European Biochemical Societies.

The calcium-dependent protein kinase CPK1 regulates a pivotal developmental switch in senescence and leaf cell death through direct phosphorylation of transcription factor ORE1.

The unicellular red alga Galdieria sulphuraria is a facultative heterotrophic member of the Cyanidiaceae, a group of evolutionary highly conserved extremophilic red algae. Uptake of various sugars and polyols is accomplished by a large number of distinct plasma membrane transporters. We have cloned three transporters [GsSPT1 (G. sulphuraria sugar and polyol transporter 1), GsSPT2 and GsSPT4], followed their transcriptional regulation and assayed their transport capacities in the heterologous yeast system. SPT1 is a conserved type of sugar/H(+) symporter with 12 predicted transmembrane-spanning domains, whereas SPT2 and SPT4 represent monosaccharide transporters, characterized by only nine hydrophobic domains. Surprisingly, all three proteins are functional plasma membrane transporters, as demonstrated by genetic complementation of a sugar uptake-deficient yeast mutant. Substrate specificities were broad and largely redundant, except for glucose, which was only taken up by SPT1. Comparison of SPT1 and truncated SPT1(Delta1-3) indicated that the N-terminus of the protein is not required for sugar transport or substrate recognition. However, its deletion affected substrate affinity as well as maximal transport velocity and released the pH dependency of sugar uptake. In line with these results, uptake by SPT2 and SPT4 was active but not pH-dependent, making a H(+) symport mechanism unlikely for the truncated proteins. We postulate SPT2 and SPT4 as functional plasma membrane transporters in G. sulphuraria. Most likely, they originated from genes encoding active monosaccharide/H(+) symporters with 12 transmembrane-spanning domains.