Nuclear DNA degradation during heterokaryon incompatibility in Neurospora crassa

Abstract In the filamentous fungus, Neurospora crassa, mating type is regulated by a single locus with alternate alleles, termed A and a. The mating type alleles control entry into the sexual cycle, but during vegetative growth they function to elicit heterokaryon incompatibility, such that fusion of A and a hypha results in death of cells along the fusion point. Previous studies have shown that the A allele consists of 5301 bp and has no similarity to the a allele; it is found as a single copy and only within the A genome. The a allele is 3235 bp in length and it, too, is found as a single copy within the a genome. Within the A sequence, a single open reading frame (ORF) of 288 amino acids (mt A-1) is thought to confer fertility and heterokaryon incompatibility. In this study, we have used repeat induced point (RIP) mutation to identify functional regions of the A idiomorph. RIP mutations in mt A-1 resulted in the isolation of sterile, heterokaryon-compatible mutants, while RIP mutations generated in a region outside of mt A-1 resulted in the isolation of mutants capable of mating, but deficient in ascospore formation.

Download Full-text

Ca2+-dependent nuclease is involved in DNA degradation during the formation of the secretory cavity by programmed cell death in fruit of Citrus grandis ‘Tomentosa’

Journal of Experimental Botany ◽

10.1093/jxb/eraa199 ◽

2020 ◽

Vol 71 (16) ◽

pp. 4812-4827 ◽

Cited By ~ 1

Author(s):

Mei Bai ◽

Minjian Liang ◽

Bin Huai ◽

Han Gao ◽

Panpan Tong ◽

...

Keyword(s):

Cell Death ◽

In Situ Hybridization ◽

Programmed Cell Death ◽

Nuclear Dna ◽

Expression Patterns ◽

Citrus Fruit ◽

Dna Degradation ◽

Secretory Cavity ◽

Spatio Temporal

Abstract The secretory cavity is a typical structure in Citrus fruit and is formed by schizolysigeny. Previous reports have indicated that programmed cell death (PCD) is involved in the degradation of secretory cavity cells in the fruit, and that the spatio-temporal location of calcium is closely related to nuclear DNA degradation in this process; however, the molecular mechanisms underlying this Ca2+ regulation remain largely unknown. Here, we identified CgCaN that encodes a Ca2+-dependent DNase in the fruit of Citrus grandis ‘Tomentosa’, the function of which was studied using calcium ion localization, DNase activity assays, in situ hybridization, and protein immunolocalization. The results suggested that the full-length cDNA of CgCaN contains an ORF of 1011 bp that encodes a protein 336 amino acids in length with a SNase-like functional domain. CgCaN digests dsDNA at neutral pH in a Ca2+-dependent manner. In situ hybridization signals of CgCaN were particularly distributed in the secretory cavity cells. Ca2+ and Ca2+-dependent DNases were mainly observed in the condensed chromatin and in the nucleolus. In addition, spatio-temporal expression patterns of CgCaN and its protein coincided with the time-points that corresponded to chromatin degradation and nuclear rupture during the PCD in the development of the fruit secretory cavity. Taken together, our results suggest that Ca2+-dependent DNases play direct roles in nuclear DNA degradation during the PCD of secretory cavity cells during Citrus fruit development. Given the consistency of the expression patterns of genes regulated by calmodulin (CaM) and calcium-dependent protein kinases (CDPK) and the dynamics of calcium accumulation, we speculate that CaM and CDPK proteins might be involved in Ca2+ transport from the extracellular walls through the cytoplasm and into the nucleus to activate CgCaN for DNA degradation.

Download Full-text

Characterization of hch , the Podospora anserina homolog of the het-c heterokaryon incompatibility gene of Neurospora crassa

Current Genetics ◽

10.1007/s002940000130 ◽

2000 ◽

Vol 38 (1) ◽

pp. 39-47 ◽

Cited By ~ 23

Author(s):

Sven J. Saupe ◽

Corinne Clavé ◽

Martine Sabourin ◽

Joël Bégueret

Keyword(s):

Neurospora Crassa ◽

Podospora Anserina ◽

Heterokaryon Incompatibility

Download Full-text

A SEARCH FOR COMPLEXITY AT THE MATING-TYPE LOCUS OF NEUROSPORA CRASSA

Canadian Journal of Genetics and Cytology ◽

10.1139/g73-069 ◽

1973 ◽

Vol 15 (3) ◽

pp. 577-585 ◽

Cited By ~ 24

Author(s):

Dorothy Newmeyer ◽

H. Branch Howe Jr. ◽

Donna R. Galeazzi

Keyword(s):

Neurospora Crassa ◽

Mating Type ◽

Adjacent Gene ◽

Opposite Mating Type ◽

Type Locus ◽

Linked Gene ◽

Heterokaryon Incompatibility ◽

Mating Type Locus ◽

Incompatibility Reaction ◽

The Right

Evidence for complexity at the mating-type locus of Neurospora crassa was sought by selecting recombinants between closely linked markers on either side. All recombinants were tested for crossing ability, to test the hypothesis that the two mating-type alleles are actually closely linked self-sterile mutants; such tests should also detect subunits analogous to the α and β subunits of the A factor of Schizophyllum or Coprinus. No change in crossing ability was found among the 5,019 recombinants tested, representing 235,000 viable ascospores. The results indicate that if subunits exist, they are not more than 0.002 units apart. Twelve hundred and forty of the recombinants were tested in a way that should also have detected subunits analogous to the A and B factors of Schizophyllum and Coprinus, except that A and B would be closely linked. No such subunits were detected.N. crassa strains of opposite mating type are heterokaryon-incompatible during vegetative growth, and observations of various investigators have suggested that the heterokaryon incompatibility might be controlled by a separate closely-linked gene rather than by mating type itself. A sample of the recombinants was therefore tested for separation of the heterokaryon-incompatibility and crossing-compatibility functions. (Heterokaryon-incompatibility was scored by the presence of an incompatibility reaction in duplications heterozygous for mating type; this technique is simple and eliminates complications due to unlinked heterokaryon-incompatibility loci, several of which are known in N. crassa.) No separation was found. The results indicate that if an adjacent gene is responsible for the heterokaryon-incompatibility, it is not more than 0.0078 units from mating type, if on the left, and not more than 0.018 units from mating type, if on the right.

Download Full-text