CaMADS1, an AGAMOUS homologue from hazelnut, produces floral homeotic conversion when expressed in Arabidopsis

CaMADS1 is a floral-specific MADS box gene of hazelnut (Corylus avellana) which, according to its sequence and expression pattern, belongs to the AGAMOUS gene sub-family. To investigate whether CaMADS1 plays a role in specifying stamen and carpel identity, this gene was ectopically expressed in Arabidopsis. The constitutive expression of CaMADS1 in transgenic plants produced the homeotic conversion of first and second whorl organs: the first whorl exhibited carpelloid sepals and the second whorl showed staminoid features. This was expected on the basis of the ABC model, according to which ectopic expression of a functional AGAMOUS (a gene of class C) orthologue would suppress the A class homeotic function in the first and second whorls, leading to transformation of these whorls into carpels and stamen, respectively. These results indicate a functional equivalency between AGAMOUS and CaMADS1, for which CaMADS1 might behave like a class C homeotic gene, controlling the determination of stamen and carpel identity in hazelnut Received: 31 July 2000 / Revision accepted: 28 September 2000     

Visualization of growth signal transduction cascades in living cells with genetically encoded probes based on Förster resonance energy transfer

Fluorescence probes based on the principle of Förster resonance energy transfer (FRET) have shed new light on our understanding of signal transduction cascades. Among them, unimolecular FRET probes containing fluorescence proteins are rapidly increasing in number because these genetically encoded probes can be easily loaded into living cells and allow simple acquisition of FRET images. We have developed probes for small GTPases, tyrosine kinases, serine–threonine kinases and phosphoinositides. Images obtained with these probes have revealed that membrane protrusions such as nascent lamellipodia or neurites provide an active signalling platform in the growth factor-stimulated cells.     

Using Co-Cultures Expressing Fluorescence Resonance Energy Transfer Based Protein Biosensors to Simultaneously Image Caspase-3 and Ca<Superscript>2+</Superscript> Signaling

Fluorescence resonance energy transfer (FRET)-based protein biosensors allow the spatial and temporal imaging of signaling events in living cells. However, the simultaneous correlation of multiple events of a signaling pathway is hindered by the spectral cross-talk between fluorescent proteins. Here, we show, for signaling pathways that progress synchronously, multiple events can be correlated by using co-cultures expressing different FRET-based protein biosensors. As a demonstration, we investigated the simultaneous caspase-3 and Ca²⁺ signaling events involved in cell death of COS-7 cells induced by 10 mM H₂O₂. Interestingly, this H₂O₂ stimulus induced synchronous caspase-3 activation and Ca²⁺ signaling. In parallel to caspase-3 activation, cytosolic Ca²⁺ concentration, [Ca²⁺]_c, gradually rises to its peak and then slowly drops. As cell shrinkage and rounding ensues, [Ca²⁺]_c again gradually rises to its peak and then reaches a plateau. These observations reveal the relative timing and location of these signaling events in cell death induced by this stimulus of H₂O₂. Finally, our approach offers an exciting opportunity for spatial and temporal imaging of multiple events in a signaling pathway in living cells.