Abstract
Understanding the growth regulatory mechanisms in filamentous fungi is very important for the production of medicines for antifungal therapies. It is well established that Ca 2+ gradient is essential for hyphal growth and that one mechanism responsible for the Ca 2+ cellular concentration starts with the hydrolysis of phosphatidylinositol 4,5bisphosphate (PIP2) by receptor-regulated forms of phosphoinositide-specific phospholipase C (PI-PLC). In the present study the levels of calcium in Aspergillus nidulans wild type (A26) and plcA-deficient mutant (AP27) growing in a carbon source readily assimilated, as glucose or pectin a non-readily assimilated carbon source was investigated. Intracellular calcium levels in A26 were higher in the presence of glucose than in pectin, but lower in AP27 independently of the carbon source and in AP27 the vesicular calcium distribution occurred mainly at the apex of the hyphae. Delay in nuclear division was also observed if A26 and AP27 were grown in pectin presence when compared with growth in glucose. For the first time, it is demonstrated that the levels of intracellular Ca 2+ were higher when A. nidulans was growing in glucose than in a non readily assimilated carbon source as pectin. Further, it also showed that the plcA gene, although not essential, may be responsible for high-molecular weight carbon source recongnation, for the intracellular Ca 2+ levels maintenance and consequently by the nuclear division in A. nidulans.
Highlights
Calcium ions act as second messengers in the signal transduction pathways in eukaryotic organisms from fungi to humans
It is known that one of the mechanisms responsible for regulating the Ca2+ cellular concentration starts with the hydrolysis of phosphatidylinositol 4,5bisphosphate (PIP2) by receptor-regulated forms of phosphoinositide-specific phospholipase C (PI-PLC) generating two products, myo-inositol 1.4.5-triphosphate (IP3) and di- -acylglycerol (DAG), which are the second messengers in the control of many cell functions [4,5,6]
As IP3, a product of a reaction catalyzed by PLC is responsible for intracellular calcium regulation, the present study describes the relations of intracellular calcium levels and two carbon sources in a mutant transformed with plcA gene rupture growing in the presence of readily or non-readily assimilated carbon source
Summary
Calcium ions act as second messengers in the signal transduction pathways in eukaryotic organisms from fungi to humans. Very little is known about the mechanisms, which coordinate morphogenesis, growth and nuclear division in fungi, mostly when they are growing in different carbon sources. Our previous results showed that two phospholipase C (E.3.1.4.3) (PLC) inhibitors delayed the first nuclear division in the A. nidulans cultures growing in the glucose presence, but stimulated it in a medium with pectin [7]. It was suggested that PLC may modulate differently the cellular signal related with the first nuclear division depending on glucose or pectin to be the carbon source present. As IP3, a product of a reaction catalyzed by PLC is responsible for intracellular calcium regulation, the present study describes the relations of intracellular calcium levels and two carbon sources in a mutant transformed with plcA gene rupture growing in the presence of readily (glucose) or non-readily (pectin) assimilated carbon source. SAID sults show for the first time the importance of carbon source and PLC in the maintenance of intracellular calcium levels and in the first stages of germination in A. nidulans
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