Identifying Genes Involved in Meristem Function

     An ongoing goal of the lab is to identify and characterize genes involved in several aspects of meristem function. One of our strategies involves performing a sensitized mutant screen in Arabidopsis, using as the source material plants that misexpress the meristem gene KNAT1 under the control of the cauliflower mosaic virus 35S promoter. Such plants form lobed leaves and initiate ectopic meristems on the leaf. We reasoned that genes that promote meristem activity would suppress the 35S::KNAT1 phenotype when mutated, resulting in reduced lobing and reduced ectopic meristem formation. Similarly, genes that restrict meristem activity would enhance the 35S::KNAT1 leaf phenotype, showing more lobes and ectopic meristems. Because of its reliance on leaf phenotypes, this screen is more rapid than traditional screens for meristem mutants, and is more likely to identify mutants in genes with redundant functions in native meristems. Also, because 35S::KNAT1 plants have limited phenotypic effects outside of the leaf, it is also possible to identify meristem genes that act independently of KNAT1, such as those involved in flower meristem function. We have isolated several mutants in each of the expected classes: enhancers, suppressors, and independent mutants, and are characterizing them in detail using genetic and molecular tools.

     In addition we are carrying out screens to identify genes involved in specific aspects of meristem function, including the role of auxin in meristem maintenance and primordia initiation, and the molecular basis of phyllotaxy and organ pattern determination.

Figure 1. Wild type Arabidopsis leaves (far left) are unlobed, but misexpression of the KNAT1 gene causes lobing of varying severity. New, ectopic meristems form in the nodes and initiate new leaves, seen on the closeup of the leaf on the right.  Click the image to view full size.

Figure 2. Examples of suppressor mutants. sok1 and sok2 mutants almost completely eliminate the lobes in leaves of 35S::KNAT1 plants. sok1 has no phenotype on its own, while sok2 leaves are much smaller than wild type. Using a sensitized screen allows us to identify a greater range of mutants than in traditional screens.  Click the image to view full size.