Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2009
Publication Date: 11/1/2009
Publication URL: http://hdl.handle.net/10113/36452
Citation: Kuppusamy, K.T., Ivashuta, S., Bucciarelli, B., Vance, C.P., Gantt, S.J., VandenBosch, K.A. 2009. Knockdown of Cell Division Cycle16 Reveals an Inverse Relationship between Lateral Root and Nodule Numbers and a Link to Auxin in Medicago truncatula. Plant Physiology. 151(3):1155-1166. Interpretive Summary: Legume plants can convert atmospheric nitrogen (N2) gas into a useful form of N fertilizer through a process known as symbiotic N2 fixation. Thus, legumes require no N fertilizer and can provide N to a subsequent crop grown in rotation. The process of N2 fixation occurs in small wart-like structures on roots known as nodules. In efforts to understand how plants make root nodules and conduct symbiotic N2 fixation, we have been identifying plant genes involved in this process. In this research we identify a gene involved in cell division, cell division cycle 16 (CDC16), as being crucial to root nodule formation and lateral root initiation. We characterized CDC16, showed where the gene was expressed, and used a special technique to knockout the expression of CDC16. When we knocked out CDC16 gene expression, fewer nodules were formed and those that did form were delayed in N2 fixation. This caused plants to grow poorly and be deficient in N. Understanding how CDC16 works will be useful in helping to improve N2 fixation and root growth. The CDC16 gene may also be a useful marker for meristem initiation.
Technical Abstract: The post-embryonic development of lateral roots and nodules is a highly regulated process. Recent studies suggest the existence of cross talk and interdependency in the growth of these two organs. Although plant hormones including auxin and cytokinin appear to be key players in coordinating this cross talk, very few genes that cross-regulate root and nodule development have been uncovered so far. This study reports that a homolog of CELL DIVISION CYCLE 16 (CDC16), a core component of the Anaphase Promoting Complex, is one of the key mediators in controlling the overall number of lateral roots and nodules. A partial suppression of this gene in Medicago truncatula leads to a decrease in number of lateral roots and a 2-4 fold increase in number of nodules. The roots showing lowered expression of MtCDC16 also show reduced sensitivity to phytohormone auxin, thus providing a potential function of CDC16 in auxin signaling.