The LLA23 protein translocates into nuclei shortly before desiccation in developing pollen grains and regulates gene expression in Arabidopsis

Abstract

We have isolated the LLA23 gene in the pollen of Lilium longiflorum. The LLA23 gene encodes an ASR (named after abscisic acid, stress and ripening) protein that has a nuclear localization sequence at the C terminus. The gene is interrupted by one single intron and possesses a long 5'-untranslated region. Southern blots of lily genomic DNA indicated that LLA23 is a member of a small gene family. We examined the link between LLA23 location and the desiccation that naturally occurs in developing anthers using immunogold labeling. When pollen reached maturity, a significant increase in LLA23 labeling was observed in the nuclei of both vegetative and generative cells from 10- to 12-cm buds and thereafter. This clearly demonstrates that a marked increase in LLA23 translocation from the cytoplasm to both nuclei of pollen grains occurs in 12-cm buds, a stage shortly before the commencement of desiccation during anther development. In addition, microarray analysis showed that 410 (206 up-regulated and 204 down-regulated) genes have altered expression in LLA23-overexpressing plants. Quantitative PCR analysis confirmed the changes in mRNA levels observed in our microarray analysis. This genome-wide overview of gene expression supports the theory that LLA23 acts as a regulator.