Abstract
Recent studies have established that boron in plant cells occurs as the borate-rhamnogalacturonan II (RG-II) complex, but the function of this complex has yet to be identified. 3-Deoxy-D-manno-oct-2-ulosonic acid (KDO) is a specific component monosaccharide of RG-II. Mutant plants defective in KDO biosynthesis are expected to have altered RG-II structure and should be useful to study the function of borate-RG-II complex. To obtain such a mutant we have been characterizing the KDO biosynthesis in Arabidopsis.
CTP:KDO cytidylyltransferase (CMP-KDO synthetase; CKS) activates KDO prior to the incorporation into RG-II. No homozygous mutants were found in the T-DNA insertion lines of this gene. Analysis using +/cks heterozygote in quartet background demonstrated that cks mutation made pollen infertile through the inhibition of pollen tube growth. Ovules were less sensitive to the mutation, but their development and/or function also seemed to be impaired under boron deficient condition. These results imply that cells can manage to grow with mutant RG-II lacking KDO, but the intact RG-II is indispensable under limited boron supply or in rapidly growing cells such as pollen tubes.
