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 corresp onding to a tapetum-specific transcript, designated as PR-10a from Lil ium longiflorum. Anther ontogeny is histologically divided into three consecutive phases. The first encompasses early proliferative stages a nd differentiation of the locules. The second concerns microspore deve lopment from the onset of meiosis through microspore maturation. The f inal phase involves pollen maturation, originating with microspore mit osis through pollen formation. The lily PR-10a transcript is anther-sp ecific and temporally expressed only at the phase of microspore develo pment during which the tapetal cells become polarized, highly secretor y, and exhibit loss of cell walls. The maximal level of PR-10a transcr ipt coincides strictly with the peak of tapetal secretory function. Co mparing mRNA and cDNA insert sizes reveals that PR-10a is close to ful l-length. Sequence analysis demonstrates similarity between the predic ted lily PR-10a and asparagus AoPR1 protein, potato pSTH2 and pSTH21 p roteins, parsley PcPR1 and PcPR3 proteins, bean PvPR1 and PvPR2 protei ns, lupin L1R 18B protein, pea I49 protein and a family of major aller gens 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, t his is the first reported organ/tissue-specific IPR protein.