Plant Biology

Making a Nodule

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Science  26 Sep 2003:
Vol. 301, Issue 5641, pp. 1815
DOI: 10.1126/science.301.5641.1815c

Many plant cells are endoploid owing to the duplication of their genome in the absence of mitosis—a process known as endoreduplication. In the legume Medicago trunculata, the nitrogen-fixing root nodule cells show particularly high amounts of endoploidy and may have 64 times the usual complement of chromosomes. Vinardell et al. examined the role of the protein CCS52A, an anaphase-promoting complex activator, in the formation of endosymbiotic nitrogen-fixing nodules. CCS52A is produced after the nodule primordium forms and is required for the final stages of nodule maturation during which the cells become polyploid. Earlier stages in nodule development, involving proliferation of meristem cells, are not affected by CCS52A. CCS52A probably promotes endoreduplication in maturing nodule cells through degradation of mitotic cyclins that would otherwise promote entry into mitosis. Cells deficient in CCS52A did not undergo endoreduplication and are refractory to infection by rhizobial bacteria. Development of mature nitrogen-fixing nodules requires a balance between plant cell endoreduplication, bacterial infection, and host-cell growth concomitant with intracellular bacteroid proliferation. — PJH

Plant Cell 15, 2093 (2003).

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