A Role for Arabinogalactan-Proteins in Root Growth
The synthetic phenylglycoside, β-glucosyl Yariv reagent (βGlcY), binds specifically to a subset of AGPs in Arabidopsis thaliana roots. When wild-type seedlings are germinated in media containing 30 μM βGlcY, a dramatic reduction in root and shoot growth, compared to control seedlings, is observed (Willats and Knox 1996). Short roots are a result of reduced cell elongation rather than reduced cell proliferation. We have used this βGlcY-phenotype in wild-type plants as a reference point in the screening of T-DNA and EMS-generated mutants for seedlings that are supersensitive or insensitive to βGlcY, or which show an altered pattern of βGlcY binding. The EMS-generated mutant, YSS1, has an apparently wild-type phenotype at 14 days. However, when YSS1 is germinated in the presence of βGlcY, the growth of the seedling is retarded to a much greater extent than wild-type seedlings, and the root is less than a millimetre in length at 14 days. This result with YSS1 is in contrast to wild-type seedlings grown in 30 μM βGlcY, where maximum root length is 8 mm. When YSS1 is transferred to medium without βGlcY, the mutant appears to recover a wild-type phenotype. This mutant, YSS1, is a very recent finding in our laboratory, and results are preliminary. It is possible, however, that YSS1 is a mutant that is supersensitive to βGlcY treatment. If this is the case, molecular studies of YSS1 are likely to yield important data regarding the βGlcY-binding subset of AGPs and their role in cell expansion.