Physiological diversity amongst tryptophan auxotrophs in Neurospora crassa

Abstract

Conidia of Ema of Neurospora crassa were treated with 1.168% concentration of formaldehyde (HCHO) for 10 minutes and 3% concentration of ethyl-methane sulphonate (EMS) for 12 hours and produced 4 types (albino, vigorous, fluffy and ropy) and 5 types (buff, conidial-band, albino, ropy and fluffy) of morphological mutants respectively. Mutants showed variation in their conidial germination, linear mycelial growth and weight of dry mycelia. UV irradiation of conidia of Ema at a wave length of 254 nm for 90 seconds produced 6 types (albino, buff, conidial-band, fluffy, ropy and vigorous) of morphological and 3 types (tryptophan, arginine and leucine) of biochemical mutants. Complementation test of all the seventeen tryptophan mutants were made with all the tryptophan standard markers trp-1a (10575), trp-2a (75001), trp-3a(C83), trp-4a (Y2198), and trp-5a (A420). It was found that four mutants belong to trp-1, seven mutants belong to trp-2, two mutants belong to trp-3, two mutants belong to trp-4 and two mutants belong to trp-5. On the basis of their specific growth requirements physiological diversity was detected amongst the seventeen tryptophan auxotrophs. The mutants fall into three categories namely anthranilic acid requiring (9 mutants), indole requiring (6 mutants) and tryptophan requiring (2 mutants). Inter allelic complementation studies of seventeen trp auxotrophs reveal that trp-1 auxotrophs comprises two heterocaryon groups (I and II) and two complons (A and B). trp-2 auxotrophs comprises three groups (I, II, III) and two complons (A and B). Auxotrophs of trp-3, trp-4 and trp-5 do not show any inter allelic complementation and no heterocaryon grouping amongst themselves. Linkage studies of seventeen auxotrophs with marker representatives of all the seven linkage groups reveal that trp-B13a, trp-B21a, trp-B41a and trp-B51a are linked with leu-1 of linkage group-III; trp-B8a, trp-12a, trp-B14a, trp-B22a, trp-B28a, trp-B38a and trp-B42a are linked with trp-2 of linkage group VI; trp-B17a and trp-B54a are linked with arg-2 of linkage group IV; trp-B5a and trp-B55a are linked with leu-5 of linkage group-5; trp-B11a and trp-B33a is linked with leu-3 of linkage group 1 and arg-5 of linkage group II respectively. Fine structure map of trp-1 with leu-1(33757) as a marker comprises about 10.120 centimorgan and fine structure map of trp-2 with lys-5(DS6-85) comprises 3.235 centimorgan. Cross feeding test of seventeen trp auxotrophs reveals three groups, Group-A, Group-B and Group-C. Nine anthranilic utilizing mutants belong to Group-A (B5a, B8a, B12a, B14a, B22a, B28a, B38a, B42a and B55a). Six indole utilizing mutants belong to Group-B (B11a, B13a, B17a, B41a, B51a and B54a). Two tryptophan utilizing mutants belong to Group-C (B21a and B33a). Group-A mutants grow in the filtrate of Group-B and Group-C. Group-B mutants grow poorly in the filtrate of Group-C only. Group-C mutants do not grow in the filtrate of either Group-A or Group-B mutants.