Up-regulation of genes encoding novel extracellular proteins during fruit set in pea.

The transition from the carpel of the flower to a developing fruit is a poorly characterized process despite its agricultural importance. We have identified two genes, GIC19 and GIC4, which are expressed after induction of pea (Pisum sativum L.) fruit set either by exogenous gibberellins or by pollination. GIC19 expression is temporally and spatially regulated, with transcripts mainly found in growing carpels and young fruit. Similar to GIC19, GIC4 expression is developmentally regulated during carpel and fruit development. However, GIC4 transcripts are found in other growing tissues throughout the plant. Analysis of their sequences and localization of fusion proteins with GFP indicate that both GIC19 and GIC4 are extracellular proteins. While GIC19 is a small proline-rich protein with no overall homology to other reported proteins. GIC4 belongs to a novel family of proteins. Our results reinforce a model of gibberellin mode of action during pea fruit set and development involving enhanced synthesis of extracellular proteins and secretory activity to provide materials and energy for cell growth.