Gibberellin-dependent induction of tomato extracellular invertase Lin7 is required for pollen development.

The tomato extracellular invertase family comprises four members with different expression patterns. Among the three invertase isoenzymes expressed in floral tissues, Lin5, Lin6 and Lin7, the expression of Lin7 was previously shown to be restricted to the tapetum and pollen. Histochemical analysis of β-glucuronidase (GUS) reporter activity shows Lin7 expression in pollen and pollen tubes of corresponding transgenic plants. The physiological relevance of the identification of gibberellin-responsive cis-acting elements for induction of the Lin7 promoter is supported by the repression of Lin7 expression in pollen grains by the gibberellin biosynthesis inhibitor paclobutrazol. Functional approaches with transgenic tomato plants establish a link between gibberellin action and invertase function in the tapetum for pollen development: both tissue-specific antisense repression of extracellular Lin7 and ectopic inactivation of the biologically active GAs by expression of a GA2-oxidase under control of the Lin7 promoter result in germination deficient pollen. These complementary findings support the idea that the GA requirement of pollen development, pollen germination and pollen tube growth are linked to energy metabolism via the regulation of an extracellular invertase as a key enzyme for carbohydrate supply via an apoplasmic pathway.