PhEXPA1, a Petunia hybrida expansin, is involved in cell wallmetabolism and in plant architecture specification

Expansins are wall-loosening proteinsthat induce wall stress relaxationand irreversible wall extensionin a pH-dependent manner. Despite asubstantial body of work has been performedon the characterization of manyexpansins genes in different plant species,the knowledge about their precisebiological roles during plant developmentremains scarce. To yield insightsinto the expansion process in Petuniahybrida, PhEXPA1, an expansin genepreferentially expressed in petal limb,has been characterized. The constitutiveoverexpression of PhEXPA1 significantlyincreased expansin activity, cellssize and organ dimensions. Moreover,35S::PhEXPA1 transgenic plants exhibitedan altered cell wall polymer compositionand a precocious timing of axillarymeristem development compared withwild-type plants. These findings supporteda previous hypothesis that expansinsare not merely structural proteinsinvolved in plant cell wall metabolismbut they also take part in many plantdevelopment processes. Here, to supportthis expansins dual role, we discussabout differential cell wall-relatedgenes expressed in PhEXPA1 expressionmutants and gradients of altered petuniabranching pattern.