Phytaspases are Asp-specific subtilisin-like plant proteases that have been likened to animal caspases with respect to their regulatory function in programmed cell death (PCD). We identified twelve putative phytaspase genes in tomato that differed widely in expression level and tissue-specific expression patterns. Most phytaspase genes are tandemly arranged on tomato chromosomes one, four, and eight, and many belong to taxon-specific clades, e.g. the P69 clade in the nightshade family, suggesting that these genes evolved by gene duplication after speciation. Five tomato phytaspases (SlPhyts) were expressed in N. benthamiana and purified to homogeneity. Substrate specificity was analyzed in a proteomics assay and with a panel of fluorogenic peptide substrates. Similar to animal caspases, SlPhyts recognized an extended sequence motif including Asp at the cleavage site. Clear differences in cleavage site preference were observed implying different substrates in vivo and, consequently, different physiological functions. A caspase-like function in PCD was confirmed for five of the seven tested phytaspases. Cell death was triggered by ectopic expression of SlPhyts 2, 3, 4, 5, 6 in tomato leaves by agro-infiltration, as well as in stably transformed transgenic tomato plants. SlPhyts 3, 4, and 5 were found to contribute to cell death under oxidative stress conditions.

Background:It is yet unknown how maize plants respond to a partial root drying under conditions of a limited total water supply, and which adaptation mechanisms are triggered under these conditions. Aims:The aims of this study were to assess whether partial root drying results in distinguishable local and systemic physiological and metabolic drought responses, and whether compensatory water uptake and/or alteration of root architecture occurs under these conditions.Methods: Maize plants were grown in a split-root system. When plants were 20 days old, the treatments 'well-watered' , 'local drought' and 'full drought' were established for a period of 10 days. Shoot length and gas exchange were measured non-destructively, root exudates were collected using a filter system and biomass, relative water content, osmolality and proline content were determined destructively at final harvest. Results:Local drought triggered stress responses such as reduced biomass, shoot length, relative water content and increased osmolality. Maintained root growth was systemically achieved by hydraulic redistribution rather than by altering root architecture. Local and systemic osmolyte adjustments contributed to this hydraulic redistribution. Conclusions:Both local and systemic metabolic responses helped the plants to induce hydraulic redistribution, enhance water availability and in consequence plant water relations. This resulted in a surprisingly well-maintained root growth even in the drought stressed root compartment.

This Article contains an error in the Methods section under subheading 'Substrate specificity of tomato phytaspases' where, "Briefly, a protein extract from Arabidopsis leaves was digested with proteomics-grade trypsin to generate a library of several thousand peptides, that were chemically modified to protect free sulfhydryl and amino groups. " should read: "Briefly, a protein extract from Arabidopsis leaves was digested with proteomics-grade chymotrypsin to generate a library of several thousand peptides, that were chemically modified to protect free sulfhydryl and amino groups. " In addition, there is an error in the legend of Figure 4 where, "Letter size reflects the relative frequency of an amino acid at a given position as compared to natural abundance in the tomato proteome. " should read: "Letter size reflects the relative frequency of an amino acid at a given position as compared to natural abundance in the Arabidopsis proteome. "