Abstract
Senescence is the final stage of plant development. Although expression of most of the genes is suppressed during senescence, a set of genes referred as senescence-associated genes (SAGs) is induced. Arabidopsis thaliana SAG12 (AtSAG12) is one such gene that has been mostly studied for its strict association with senescence. AtSAG12 encodes a papain-like cysteine protease, expressed predominantly in senescence-associated vacuoles. Rice genome contains multiple AtSAG12 homologues (OsSAGs). OsSAG12-1, the closest structural homologue of AtSAG12, is a negative regulator of developmental and stress-induced cell death. Proteolytic activity has not been established for any SAG12 homologues in vitro. Here, we report that OsSAG12-2, the second structural homologue of AtSAG12 from rice, codes for a functional proteolytic enzyme. The recombinant OsSAG12-2 protein produced in Escherichia coli undergoes autolysis to generate a functional protease. The matured OsSAG12-2 protein shows 27% trypsin-equivalent proteolytic activity on azocasein substrate. Dark-induced senescence activates OsSAG12-2 expression. Down-regulation of OsSAG12-2 in the transgenic artificial miRNA lines results in enhanced salt- and UV-induced cell death, even though it does not affect cell viability in the stress-free condition. Our results show that OsSAG12-2 codes for a functional protease that negatively regulates stress-induced cell death in rice.
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Acknowledgements
We acknowledge Kang Chong, Institute of Botany, Chinese Academy of Science, Beijing, for providing pTCK303 vector. This work is supported by DST grant (SR/SO/PS-29/2006) and DST-PURSE to AKN; CSIR fellowship to SS; and UGC fellowship to AS.
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Corresponding editor: Utpal Nath
[Singh S, Singh A and Nandi AK 2016 The rice OsSAG12-2 gene codes for a functional protease that negatively regulates stress-induced cell death. J. Biosci.]
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Singh, S., Singh, A. & Nandi, A.K. The rice OsSAG12-2 gene codes for a functional protease that negatively regulates stress-induced cell death. J Biosci 41, 445–453 (2016). https://doi.org/10.1007/s12038-016-9626-9
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DOI: https://doi.org/10.1007/s12038-016-9626-9