Characterization of a lily tapetal transcript that shares sequence similarity with a class of intracellular pathogenesis-related (IPR) proteins

This study addresses isolating and characterizing a cDNA clone corresponding to a tapetum-specific transcript, designated as PR-10a from Lilium longiflorum. Anther ontogeny is histologically divided into three consecutive phases. The first encompasses early proliferative stages and differentiation of the locules. The second concerns microspore development from the onset of meiosis through microspore maturation. The final phase involves pollen maturation, originating with microspore mitosis through pollen formation. The lily PR-10a transcript is anther-specific and temporally expressed only at the phase of microspore development during which the tapetal cells become polarized, highly secretory, and exhibit loss of cell walls. The maximal level of PR-10a transcript coincides strictly with the peak of tapetal secretory function. Comparing mRNA and cDNA insert sizes reveals that PR-10a is close to full-length. Sequence analysis demonstrates similarity between the predicted lily PR-10a and asparagus AoPR1 protein, potato pSTH2 and pSTH21 proteins, parsley PcPR1 and PcPR3 proteins, bean PvPR1 and PvPR2 proteins, lupin L1R 18B protein, pea I49 protein and a family of major allergens including Cor a 1 of hazel, Car b 1 of hornbeam, Aln g 1 of alder, Bet v 1 of birch and Api g 1 of celery. To the authors' knowledge, this is the first reported organ/tissue-specific IPR protein.