Abstract
An abundant 17 kDa RNase, encoded by OsPR10a (also known as PBZ1), was purified from Pi-starved rice suspension-cultured cells. Biochemical analysis showed that the range of optimal temperature for its RNase activity was 40–70°C and the optimum pH was 5.0. Disulfide bond formation and divalent metal ion Mg2+ were required for the RNase activity. The expression of OsPR10a::GUS in transgenic rice was induced upon phosphate (Pi) starvation, wounding, infection by the pathogen Xanthomonas oryzae pv. oryzae (Xoo), leaf senescence, anther, style, the style-ovary junction, germinating embryo and shoot. We also provide first evidence in whole-plant system, demonstrated that OsPR10a-overexpressing in rice and Arabidopsis conferred significant level of enhanced resistance to infection by the pathogen Xoo and Xanthomona campestris pv. campestris (Xcc), respectively. Transgenic rice and Arabidopsis overexpressing OsPR10a significantly increased the length of primary root under phosphate deficiency (-Pi) condition. These results showed that OsPR10a might play multiple roles in phosphate recycling in phosphate-starved cells and senescing leaves, and could improve resistance to pathogen infection and/or against chewing insect pests. It is possible that Pi acquisition or homeostasis is associated with plant disease resistance. Our findings suggest that gene regulation of OsPR10a could act as a good model system to unravel the mechanisms behind the correlation between Pi starvation and plant-pathogen interactions, and also provides a potential application in crops disease resistance.
Highlights
In order to survive during phosphate (Pi) starvation, plants have evolved the ability to increase the efficiency of Pi uptake via the up-regulation of a wide variety of intra- and extra-cellular ribonucleases (RNases) so as to scavenge and recycle Pi from organic phosphorus compounds [1]
Research has successfully identified at least five PR10-like genes/proteins in rice that respond to biotic stresses, such as pathogen infection [17,18,19,20,21,22], jasmonic acid (JA) and salicylic acid (SA) [23,24,25], or the expression of which are induced by abiotic stresses, including salt and drought [21,25,26]; the first identified gene/protein of this type was OsPR10a/PBZ1 [17]
In a gel containing yeast t-RNA, a clear zone at around 17 kDa was detected in both +Pi- and -Pitreated cells (Fig 1B), but much higher activity was observed in protein extracts isolated from -Pi than +Pi-treated cells, indicating that the RNase activity was induced under Pi starvation
Summary
In order to survive during phosphate (Pi) starvation, plants have evolved the ability to increase the efficiency of Pi uptake via the up-regulation of a wide variety of intra- and extra-cellular ribonucleases (RNases) so as to scavenge and recycle Pi from organic phosphorus compounds [1]. Secretomic analysis identified an extracellular ribonuclease 1 (RNS1) lacking the putative N-terminal signal peptide in Pi-starved Arabidopsis suspension cells [6] These studies indicated that ribonucleases play a key role in Pi scavenging and recycling from extra- and intra-cellular ribonucleic acids under phosphate starved (-Pi) conditions. Plant pathogenesis-related (PR) proteins are expressed in response to pathogen infection, environmental stresses and developmental processes, and some of them are expressed constitutively [7,8] They can be divided into at least 17 different groups, PR-1 to -17, according to their amino acid sequences, immunological relationships and biological activities [9,10,11]. There have been only limited in vivo studies on the roles of PR10-related proteins in resistance to pathogen attack and the results remain to be verified
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