Plant plasma membrane-bound staphylococcal-like DNases as a novel class of eukaryotic nucleases

Abstract

BackgroundThe activity of degradative nucleases responsible for genomic DNA digestion has been observed in all kingdoms of life. It is believed that the main function of DNA degradation occurring during plant programmed cell death is redistribution of nucleic acid derived products such as nitrogen, phosphorus and nucleotide bases. Plant degradative nucleases that have been studied so far belong mainly to the S1-type family and were identified in cellular compartments containing nucleic acids or in the organelles where they are stored before final application. However, the explanation of how degraded DNA components are exported from the dying cells for further reutilization remains open.ResultsBioinformatic and experimental data presented in this paper indicate that two Arabidopsis staphylococcal-like nucleases, named CAN1 and CAN2, are anchored to the cell membrane via N-terminal myristoylation and palmitoylation modifications. Both proteins possess a unique hybrid structure in their catalytic domain consisting of staphylococcal nuclease-like and tRNA synthetase anticodon binding-like motifs. They are neutral, Ca2+-dependent nucleaces showing a different specificity toward the ssDNA, dsDNA and RNA substrates. A study of microarray experiments and endogenous nuclease activity revealed that expression of CAN1 gene correlates with different forms of programmed cell death, while the CAN2 gene is constitutively expressed.ConclusionsIn this paper we present evidence showing that two plant staphylococcal-like nucleases belong to a new, as yet unidentified class of eukaryotic nucleases, characterized by unique plasma membrane localization. The identification of this class of nucleases indicates that plant cells possess additional, so far uncharacterized, mechanisms responsible for DNA and RNA degradation. The potential functions of these nucleases in relation to their unique intracellular location are discussed.

IREN, a novel EF-hand motif-containing nuclease, functions in the degradation of nuclear DNA during the hypersensitive response cell death in rice

“…Arabidopsis CAN1 and CAN2 nucleases are neutral, Ca 2+ -dependent nucleases displaying different specificities toward single-stranded DNA, double-stranded DNA, and RNA substrates. 53) In this study, we showed that IREN activity is slightly activated in the presence of Ca 2+ or in the presence of Mg 2+ /Mn 2+ , but is strongly activated in the presence of both Ca 2+ and Mg 2+ . In addition, IREN was inhibited by Zn 2+ and degraded both single-stranded and double-stranded DNA (data not shown).…”

The importance of lipid modified proteins in plants

“…N‐myristoylated and S‐acylated proteins include well‐known proteins such as many of the calcium‐dependent protein kinases (CPKs; Martin & Busconi, ) and calcineurin‐B like proteins (CBLs; Batistic et al ., ), the heterotrimeric G‐protein α‐subunit GPA1 (Adjobo‐Hermans et al ., ), receptor‐like cytoplasmic kinases (Hemsley et al ., ; Liu et al ., ) and more unexpected groups of proteins such as group 3 h ‐Thioredoxins ( h ‐TRX; Hemsley et al ., ; Traverso et al ., ). An entirely novel class of Ca 2+ ‐dependent nucleases typified by the CAN1 and CAN2 proteins of Arabidopsis has been proposed to be N‐myristoylated and S‐acylated (Lesniewicz et al ., ), a finding that was subsequently confirmed for S‐acylation (Hemsley et al ., ). These nucleases are found at the PM, an entirely unique localisation for this class of proteins, although the importance of this localisation in their function has yet to be described (Lesniewicz et al ., ).…”

“…An entirely novel class of Ca 2+ ‐dependent nucleases typified by the CAN1 and CAN2 proteins of Arabidopsis has been proposed to be N‐myristoylated and S‐acylated (Lesniewicz et al ., ), a finding that was subsequently confirmed for S‐acylation (Hemsley et al ., ). These nucleases are found at the PM, an entirely unique localisation for this class of proteins, although the importance of this localisation in their function has yet to be described (Lesniewicz et al ., ). Interestingly, some bacterial type‐III secreted effector proteins are N‐myristoylated and S‐acylated once inside the host cell by the host machinery.…”

Palmitoylation in plants

“…In recent years S-acylation in plants has begun to come of age with the enzymes responsible for S-acylation being identified and characterized, [2][3][4] in-depth analysis of the role of S-acylation in the function of ROP GTPases, 5-8 many other S-acylated proteins recently being described [9][10][11][12] and tools to analyze S-acylation being developed. 7,13 Despite the important properties of S-acylation and increased interest in its function, it is still very difficult to predict whether a protein is S-acylated.…”