Petal abscission in rose (Rosa bourboniana var Gruss an Teplitz) is associated with the enhanced expression of an alpha expansin gene, RbEXPA1

Abscission is a process that involves separation of the organ from the parent plant. In this paper we show that the progressive abscission of petals, commonly observed post-pollination is sensitive to treatment with ethylene in the fragrant varieties of Rosa bourboniana (var Gruss an Teplitz). We also provide the first evidence that the expression of the expansin gene is associated with petal abscission not only under ethylene-induced conditions but also under natural conditions. The gene, RbEXPA1, encodes for a putative protein of 253 amino acids with essential features conserved as in other alpha expansins. The expression of RbEXPA1 increases in abscission zones of petals during the course of natural abscission and post-ethylene treatment. Treatment of flowers with 1-methyl cyclopropene (an ethylene perception inhibitor) results in a delay in abscission and is associated with a simultaneous reduction in the expression of RbEXPA1. Flowers require a longer time for petal abscission under field conditions, and this is correlated with a delay in expression of RbEXPA1 as compared to ethylene treated flowers. Transcript accumulation is specific to petals and is enhanced in response to ethylene. The enhancement in expression is more prominent in the petal abscission zones than in whole petals. Expression of RbEXPA1 is not observed during development of the flower and petal expansion indicating that it is not an expansion related gene. It is concluded that transcriptional up regulation of the ethylene sensitive expansin gene may help in wall modification leading to petal abscission in rose.