Functional analysis of genes associated with flower senescence

In the past decade researchers have reported increasingly comprehensive cDNA libraries of genes associated with floral senescence in floral crops. Analysis of the function of these genes in flower senescence has depended on the slow process of stable transformation and regeneration of the plants. We have adopted an alternative strategy, using virus-induced gene silencing (VIGS) to evaluate the effects on flower senescence of silencing senescence-associated gene. Using purple flowered petunia as our test organism, we infect with a construct where the RNA2 of tobacco rattle virus (TRV) is modified by insertion of chalcone synthase (CHS, a key enzyme in anthocyanin biosynthesis). When virus infection occurs, the plant's silencing mechanism silences CHS, resulting in white sectors or flowers. Infection with TRV containing a tandem construct of phytoene desaturase (PDS) and CHS resulted in characteristic photobleaching of leaves (due to impaired carotene synthesis), and white patterns on the flowers. Transcripts of CHS and PDS were reduced both in leaves and in flowers confirming simultaneous silencing of both genes by the tandem construct. We tested the effects of infection with TRV containing CHS and a fragment of a petunia gene encoding for 1-aminocyclopropane-1-carboxylate oxidase (ACO). Whether the flowers were treated with ACC or pollinated, the white (silenced) sectors produced less ethylene and senesced later than the purple sectors. These results indicate the value of VIGS with tandem constructs containing CHS as reporter and a target gene as a tool for examining the function of genes isolated from senescing floral tissues.