Biochemical characterization of a pollen-specific cDNA encoding polygalacturonase in Lilium longiflorum

A pollen-specific transcript, designated LLP-A1.1, in lily (Lilium longiflorum Thunb. cv. Snow Queen) plants was isolated and characterized. The full-length cDNA encodes polygalacturonase (PG) having a sequence of 413 amino acids, a calculated molecular mass of 44 kDa, and a calculated pI of 8.1. Assessment of the hydropathy shows that the protein contains a hydrophobic segment at the N-terminus, indicating the presence of a putative signal peptide. The LLP-PG sequence displays significant resemblance to known pollen PG from various species and a group of major allergens including Phl p 13 of timothy grass and Pla a 2 of London planetree. Antiserum was raised against the overexpressed rLLP-PG protein in E. coli. Affinity-purified antibodies were prepared from antiserum to investigate the specificity and distribution of the protein during development. Immunoblot analyses of total protein from floral and vegetative organs confirmed that LLP-PG accumulated to detectable levels only in a discrete stage of anther development. It is a heterogeneous glycoprotein, consisting of four major and two minor polypeptides. Premature drying of developing anthers indicated that the lily LlpPG gene expression was not induced by desiccation that naturally occurs in pollen prior to anthesis.