Dual genetic pathways controlling nodule number in XXXX .

@entity4166 @entity281 @entity1786
We report the isolation and characterization of a new @entity4166 hyper-nodulation mutant, designated sunn (super numeric nodules). Similar to the previously described @entity1786 -insensitive mutant sickle, sunn exhibits a 10-fold increase in the number of nodules within the primary nodulation zone. Despite this general similarity, these two mutants are readily distinguished based on anatomical, genetic, physiological, and molecular criteria. In contrast to sickle, where insensitivity to @entity1786 is thought to be causal to the hyper-nodulation phenotype (R.V. Penmetsa, D.R. Cook [1997] Science 275: 527-530), nodulation in sunn is normally sensitive to @entity1786 . Nevertheless, sunn exhibits seedling root growth that is insensitive to @entity1786 , although other aspects of the @entity1786 triple response are normal; these observations suggest that hormonal responses might condition the sunn phenotype in a manner distinct from sickle. The two mutants also differ in the anatomy of the nodulation zone: Successful @entity281 and nodule development in sunn occur predominantly opposite xylem poles, similar to wild type. In sickle, however, both @entity281 and nodulation occur randomly throughout the circumference of the developing root. Genetic analysis indicates that sunn and sickle correspond to separate and unlinked loci, whereas the sunn/skl double mutant exhibits a novel and additive super-nodulation phenotype. Taken together, these results suggest a working hypothesis wherein sunn and sickle define distinct genetic pathways, with skl regulating the number and distribution of successful @entity281 events, and sunn regulating nodule organogenesis.
