A Pollen-Specific and Desiccation-Associated Transcript in Lilium longiflorum during Development and Stress

A cDNA clone encoding a desiccation-induced protein (LLA23) has been isolated from the mature pollen of a Lilium longiflorum cDNA library. Sequence analysis revealed significant similarity between the predicted LLA23 polypeptide, particularly at the C-terminal half of the sequence and a group of water-deficit/ripening-induced proteins. The expression of LLA23 gene is pollen-specific and the transcript accumulates only at the later stage of pollen maturation prior to anthesis. Premature drying of developing pollen confirmed that the accumulation of LLA23 transcripts was associated with desiccation. The LLA23 proteins decreased their levels when pollen/pollen tubes grew in the germination buffer. Treatments of pollen with abscisic acid (ABA) and polyethylene glycol (PEG)-8000 during germination greatly retarded the disappearance of LLA23 proteins and mRNAs. The LLA23 transcripts decreased their levels in pollen tubes grown both in vitro and in vivo, but the disappearance of LLA23 transcripts in tube cells grown in vivo was slower than those grown in vitro. In situ localization using anti-chicken immunoglobulin G conjugated with gold particles confirmed that LLA23 was located in the cytoplasm of pollen grains. The protective function of the desiccation-related proteins in the cytoplasm of pollen grains is proposed.