Genetic components of fruit body morphogenesis

1. Genetic components of fruit body morphogenesis David Moore & Siu Wai Chiu University of Manchester & The Chinese University of Hong Kong

2. Genetic and physiological nature of morphogenetic control during initiation and development of fungal fruit bodies David Moore School of Biological Sciences The University of Manchester

3. Fungal mycelium has a number of alternative developmental pathways open to it • continuation of hyphal growth • production of asexual structures • progress into the sexual cycle

4. These are not strict alternatives • a culture may express all of these possibilities • so, genetic control must be local

5. Classic genetic approaches are: • identification of variant strains • complementation tests to establish functional cistrons • heterokaryons to determine dominance • epistatic relationships in heterokaryons (to indicate the sequence of gene expression)

6. Perithecium formation in Sordaria

7. For the fruit bodies of basidiomycetes the picture is more complex • this includes mushrooms, toadstools, bracket fungi, puff-balls, stinkhorns and bird's nest fungi

9. Developmental mutants induced in mycelium of a Coprinus cinereus dikaryon - 1 • knotless, no hyphal aggregations formed • primordiumless, aggregations formed but did not develop further • maturationless, primordia produced but failed to mature

10. Developmental mutants induced in mycelium of a Coprinus cinereus dikaryon - 2 • elongationless, stem failed to elongate but cap development was normal • expansionless, stem elongation normal but cap failed to open • sporeless, few or no spores formed in otherwise normal fruit bodies

14. Normal morphogenesis is made up of developmental subroutines • subroutines for hymenophore, hymenium, stem, cap, etc. • subroutines can be put into operation independently of one another • under separate genetic control • under separate physiological control

15. Control of fungal morphogenesis Molecular models which might account for these features are: • translational triggering • feedback fixation

16. Translational triggering: a mechanism which can relate morphogenesis to competence, and to response to environmental signals

17. Translational triggering • competent state achieved and differentiation transcripts are produced • trigger-ORF translation allows downstream sequences to assume secondary structure that blocks their translation

18. Translational triggering • a specific check to growth causes ribosomes to stall at trigger-ORF • RNA assumes an alternative secondary structure which allows downstream translation

19. Translational triggering The ‘check to growth’ might be caused by • illumination • temperature shock • nutritional crisis • injury • edge encounter • extracellular matrix signal • other factors

20. Feedback fixation • Feedback activation reinforces expression of the whole regulatory pathway to make it independent of the external environmental cues which initiated it

21. Feedback fixation • where control of expression is ‘fuzzy’ being reinforced by external signals

22. Feedback fixation • where control of expression is ‘crisp’ and independent of external signals in committed cells

23. Feedback fixation • feedback fixation results in developmental determination in the classic embryological sense

24. Control of fungal morphogenesis The key to fungal morphogenesis lies in understanding how that which is outside a hypha can influence what goes on inside the hypha in a time- and place-dependent manner

25. For the full story ... • Moore, D. (1998). Presidential Address. Mushrooms upright, sideways and inside-out. Mycological Research 102, 641-657 • Moore, D. (1998). Fungal Morphogenesis. A volume in the Developmental and Cell Biology series for Cambridge University Press: New York