Expression of AtCAN1 and AtCAN2 genes of the plant SNc nuclease family correlates with programmed cell death and endoreduplication, indicating their role in the recycling of nucleic acid components
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Background
Controlled degradation of genomic DNA is a common phenomenon observed in all known cases of programmed cell death (PCD) in both animals and plants. In plants, nucleic acid degradation during PCD facilitates the redistribution of their constituent building blocks. Previous studies have shown that nucleases from the S1/P1 family are involved in this process; however, due to its complexity, it has been hypothesized that nucleases from other families, including staphylococcal-like nucleases (SNc), may also participate. In Arabidopsis , this family comprises two nucleases with an atypical plasma membrane localization for this type of enzymes: AtCAN1 and AtCAN2.
Results
Using the promoter-driven GUS reporter assay, we showed that the genes encoding SNc nucleases are expressed in tissues that can be grouped into three main categories. The first category includes plant structures that are clear examples of organs undergoing PCD, such as the root cap, vascular bundle elements, the tapetum, maturing seed pods, and senescent leaves. The second category comprises cells whose function involves interaction with the external environment and which are susceptible to pathogen attack. This group includes root hairs, stomatal guard cells, and hydathodes. The third group of plant structures showing SNc nuclease activity consists of elements characterized by endoreduplication, i.e., stipules, trichomes, and the basal parts of the hypocotyl.
Conclusions
Our studies show that SNc nucleases are as broadly involved in the DNA degradation during plant PCD as the previously reported S1/P1 proteins. The frequent overlap in their expression profiles suggests cooperative action. Whereas SNc nucleases localize to the plasma membrane, S1/P1 nucleases are nuclear, indicating distinct yet complementary nucleolytic pathways. We further demonstrate that SNc nucleases are specifically expressed in organs not undergoing PCD but characterized by endoreduplication, implicating them in an unexplored mechanism for redistributing polyploid DNA components.
