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A gene,imz, affecting the pH sensitivity of zygote formation inPhysarum polycephalum
T M Shinnick1, D J Pallotta, Y R Jones-Brown
1Scripps Clinic and Research Foundation, 10666 N. Torrey Pines Road, 92037, La Jolla, California, USA.
Abstract:
Mating inPhysarum polycephalum involves the fusion of two haploid amoebae and the differentiation of the resulting diploid zygote into a multinucleate plasmodium. Mating proceeds optimally with amoebae growing on an agar medium at pH 5.0. At pH 6.2, the amoebae still grow normally, but mating is completely blocked. The barrier at pH 6.2 is not in the differentiation step, since preformed diploids readily convert to plasmodia at this pH. The barrier can be overcome by raising the ionic strength of the agar medium; the effect, moreover, is not ion-specific. We have discovered a genetic locus,imz (ionicmodulation of zygote formation), that affects the upper pH limit for mating; the respective limits associated with the two known alleles,imz-1 andimz-2, are pH 5.6 and pH 6.0 at low ionic strength. Animz-1×imz-2 mating displays the pH 6.0 limit;imz-2 is therefore "dominant". We suggest that this new gene affects a cell component that is exposed to the exterior of the amoeba and is involved in the fusion step of mating.
Insights
Physarum polycephalum mating is blocked at pH 6.2, but can be restored by increasing ionic strength. A new gene, imz (ionic modulation of zygote formation), influences the pH limit for successful mating.
Area of Science:
- Cell Biology
- Mycology
- Genetics
Background:
- Mating in Physarum polycephalum involves haploid amoebae fusion and diploid zygote differentiation into a plasmodium.
- Optimal mating occurs at pH 5.0, with complete blockage observed at pH 6.2, despite normal amoebae growth.
Purpose of the Study:
- To investigate the pH-dependent mating barrier in Physarum polycephalum.
- To identify genetic factors controlling the upper pH limit for mating.
Main Methods:
- Physarum polycephalum mating experiments were conducted across a range of pH and ionic strengths.
- Genetic analysis was performed to identify loci affecting mating pH limits.
Main Results:
- The mating block at pH 6.2 is not due to impaired diploid differentiation but affects the initial fusion step.
- Increasing ionic strength of the medium overcomes the pH barrier in an ion-non-specific manner.
- A genetic locus, imz (ionic modulation of zygote formation), was identified, with alleles imz-1 and imz-2 defining pH limits of 5.6 and 6.0, respectively.
Conclusions:
- The imz gene likely encodes a cell surface component involved in the amoebae fusion during mating.
- Ionic strength modulates the activity or accessibility of this cell surface component, thereby influencing the pH limit for mating.
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