Induction of an Extracellular Cyclic Nucleotide Phosphodiesterase as an Accessory Ribonucleolytic Activity during Phosphate Starvation of Cultured Tomato Cells

Abstract

During growth under conditions of phosphate limitation, suspension-cultured cells of tomato (Lycopersicon esculentumMill.) secrete phosphodiesterase activity in a similar fashion to phosphate starvation-inducible ribonuclease (RNase LE), a cyclizing endoribonuclease that generates 2:3-cyclic nucleoside monophosphates (NMP) as its major monomeric products (T. Nü rnberger, S. Abel, W. Jost, K. Glund [1990] Plant Physiol 92: 970-976). Tomato extracellular phosphodiesterase was purified to homogeneity from the spent culture medium of phosphate-starved cells and was characterized as a cyclic nucleotide phosphodiesterase. The purified enzyme has a molecular mass of 70 kD, a pH optimum of 6.2, and an isoelectric point of 8.1. The phosphodiesterase preparation is free of any detectable deoxyribonuclease, ribonuclease, and nucleotidase activity. Tomato extracellular phosphodiesterase is insensitive to EDTA and hydrolyzes with no apparent base specificity 2:3-cyclic NMP to 3-NMP and the 3:5-cyclic isomers to a mixture of 3-NMP and 5-NMP. Specific activities of the enzyme are 2-fold higher for 2:3-cyclic NMP than for 3:5-cyclic isomers. Analysis of monomeric products of sequential RNA hydrolysis with purified RNase LE, purified extracellular phosphodiesterase, and cleared ؊Pi culture medium as a source of 3-nucleotidase activity indicates that cyclic nucleotide phosphodiesterase functions as an accessory ribonucleolytic activity that effectively hydrolyzes primary products of RNase LE to substrates for phosphate-starvationinducible phosphomonoesterases. Biosynthetical labeling of cyclic nucleotide phopshodiesterase upon phosphate starvation suggests de novo synthesis and secretion of a set of nucleolytic enzymes for scavenging phosphate from extracellular RNA substrates.

Phosphatase activity in temperate pasture soils: Potential regulation of labile organic phosphorus turnover by phosphodiesterase activity

“…There is evidence that nucleic acid degradation in soil is mediated primarily by Gram negative bacteria similar to Pseudomonas (Greaves and Wilson, 1970), while actinomycetes appear to be the main group of organisms responsible for degrading phospholipids (Ko and Hora, 1970). Some plants also secrete phosphodiesterase under conditions of severe Pdeficiency (Abel et al, 2000), but this probably makes a negligible contribution to the total phosphodiesterase activity in most soils.…”

Phosphate or phosphite addition promotes the proteolytic turnover of phosphate‐starvation inducible tomato purple acid phosphatase isozymes

“…Confirmation that SAP1 and SAP2 are their genuine physiological substrates awaits the purification and kinetic characterization of both proteases. It will also be of interest to assess whether extracellular Pi-inducible proteases degrade additional hydrolytic enzymes that are specifically secreted into the CCF by )Pi tomato cell cultures, namely PSI ribonucleases and phosphodiesterases [2,14,20,21]. Although the functional importance of Pi-inducible secreted proteases in response to Pi-sensing and turnover of extracellular PSI proteins remains to be determined, the current study presents the first evidence for protease upregulation in response to Pi-resupply of )Pi plants.…”

“…tomato suspension cells Pi starvation of cultured tomato cells elicits the secretion of PSI ribonucleases, phosphodiesterases and APs which collectively facilitate Pi scavenging from extracellular nucleic acids [1,2,8,9,14,20,21]. Conversely, the coordinated repression of a PSI gene (LEPS2) and degradation of the corresponding mRNA transcripts occurred within 12 h of Pi-resupply to )Pi tomato seedlings [22].…”

Analysis of the role of RNS2 and autophagy in the turnover of ribosomal RNA in Arabidopsis thaliana

“…28 Mutations in ATG5 have been shown to block macroautophagy, selective macroautophagy of protein aggregates, and microautophagy mechanisms in plants and other eukaryotes. 28,[37][38][39][40][41] rns2-2 has a T-DNA insertion in the fifth intron and is null for RNS2 RNase activity.…”

“…6,8,25 Fusion of this protein with GFP allows visualization of autophagosomes present in the cytoplasm and autophagic bodies present in the vacuole; thus GFP-ATG8 has been used extensively as an autophagosome and autophagic body marker. [26][27][28] It was unknown if the potential accumulation of autophagosomes observed in rns2-2 was a result of increased autophagosome formation or decreased autophagic body degradation in the vacuole. To differentiate between these two possibilities, vacuolar degradation was inhibited with concanamycin A (ConA).…”