EVALUATION OF 515 EXPRESSED SEQUENCE TAGS OBTAINED FROM GUARD-CELLS OF BRASSICA-CAMPESTRIS

As an attempt to examine the transcripts expressed in a single cell ty pe and to unveil the physiology of guard cells at the molecular level, we generated 515 expressed sequence tags (ESTs) from a directional cD NA library constructed from guard-cell protoplasts of Brassica campest ris L. ssp. pekinensis. A comparative analysis of the guard-cell ESTs against the National Center for Biotechnological Information nonredund ant protein database revealed that 133 ESTs (26%) have significant sim ilarity to protein coding sequences in the database. Among them were 3 5 clones related to genes that have not yet been identified in higher plants. Analysis of RNA gel blots of 14 database-matched clones reveal ed that five clones harbor the sequences for mRNAs expressed most abun dantly in guard cells, one of them detecting an mRNA with highly prefe rential expression in guard cells. Functional categorization of the pu tatively identified guard-cell ESTs showed, when compared with maize l eaf ESTs, that guard cells expressed a higher proportion of signal tra nsduction components and a lower proportion of structural or photosynt hetic genes, as is consistent with the roles of guard cells.