Expression of polyamine biosynthesis genes during parthenocarpic fruit development in Citrus clementina

Polyamines have been attributed a general role in fruit development in several plants like pea and tomato. To investigate the involvement of these compounds in parthenocarpic fruit development in Citrus clementina, we have isolated three genes encoding aminopropyl transferases in this species: CcSPDS, CcSPM1 and CcACL5. The unambiguous identity of the proteins encoded by these genes was confirmed by phylogenetic analysis and by heterologous expression in yeast mutants deficient in aminopropyl transferase activity. The expression of these genes in C. clementina is not restricted to ovaries and fruits, but it is also detectable all throughout the plant. More importantly, gibberellin-induced parthenocarpic fruit set caused a decrease in CcSPDS expression in ovaries, paralleled by a decrease in spermidine; while the expression of CcSPM1 and CcACL5 was basically unaffected, resulting in the maintenance of spermine concentration during early fruit development. In addition, the variation in putrescine content was paralleled by changes in the expression of one of the two putative CcODC paralogs.