Abstract
The postembryonic 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 CYCLE16 (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 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.
Highlights
The postembryonic development of lateral roots and nodules is a highly regulated process
To overcome the problem of the gametophytic lethality resulting from CELL DIVISION CYCLE16 (CDC16) knockout, as seen from analysis of an insertional mutation in Arabidopsis (Kwee and Sundaresan, 2003) we undertook an RNA interference (RNAi) approach to partially suppress the expression of CDC16 gene in Agrobacterium rhizogenestransformed roots of M. truncatula
We report that roots transformed with the CDC16 RNAi construct displayed a decreased sensitivity to auxin, defective primary root growth, and fewer lateral roots
Summary
The postembryonic development of lateral roots and nodules is a highly regulated process. This study reports that a homolog of CELL DIVISION CYCLE16 (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. T-DNA insertions in the Arabidopsis CELL DIVISION CYCLE16 (CDC16) and APC2 genes result in gametophytic lethality due to the failure to degrade mitotic cyclins (Capron et al, 2003b; Kwee and Sundaresan, 2003). Consistent with this, localized application of synthetic auxin transport inhibitors on alfalfa (Medicago sativa) roots induces pseudonodules (Hirsch et al, 1989) Complementing these findings, a more recent study in M. truncatula has demonstrated that increased auxin transport, caused by silencing the flavonoid pathway, results in reduced nodule formation in response to rhizobia (Wasson et al, 2006). This work highlights the importance of CDC16 in root and nodule development and indicates a possible role for this gene in auxin signaling
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