PPF-1, a post-floral-specific gene expressed in short-day-grown G2 pea, may be important for its never-senescing phenotype.

We cloned a developmentally regulated gene from a cDNA library constructed from short-day (SD) grown G2 pea tissue using cDNA representational difference analysis (cDNA RDA) and named it PPF-1 for the first Pisum sativum post-floral-specific gene. Sequence comparisons with various databases revealed that PPF-1 shares a substantial homology only at the deduced amino-acid level with the Bacillus subtilis gene SP3J, which is required for maintaining vegetative growth, and with other genes coding for bacterial inner membrane proteins. All five potential hydrophobic regions from the bacterial proteins were maintained in the PPF-1 sequence. A series of Northern blots showed that this gene was only expressed after floral initiation and was limited to the apical buds, with non-detectable levels in roots, stems and mature leaves. Under SD conditions, when G2 pea displays an unlimited growth habit, PPF-1 expression was sustained at a relatively high level long after floral initiation. Under long-day (LD) conditions, when G2 pea undergoes an apical senescence similar to wild-type plants with genotype sn hr, PPF-1 was only expressed very briefly after flower initiation. Interestingly, in day-neutral, wild-type Alaska pea, the PPF-1 level was hardly detectable under any growth conditions. Treatment of LD-grown G2 pea with gibberellin A3 (GA3) was able to stimulate PPF-1 expression unless it was applied at a very late growth stage, at which time the process of apical senescence cannot be reversed.