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ARS Home » Plains Area » Fargo, North Dakota » Edward T. Schafer Agricultural Research Center » Cereal Crops Research » Research » Publications at this Location » Publication #262778
Title: Altering sexual reproductive mode by interspecific exchange of MAT loci

Author
item Lu, Shunwen
item YUN, SUNG-HWAN - Soonchunhyang University
item LEE, THERESA - National Academy Of Agricultural Science
item TURGEON, B. GILLIAN - Cornell University

Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2011
Publication Date: 4/14/2011
Citation: Lu, S., Yun, S., Lee, T., Turgeon, B. 2011. Altering sexual reproductive mode by interspecific exchange of MAT loci. Fungal Genetics and Biology. 48:714-724.

Interpretive Summary: In ascomycete fungi, a single mating type (MAT) locus controls the ability to reproduce sexually, in two distinct ways: heterothallic mating, which occurs between two individuals of the same species that have opposite mating type genes (MAT1-1 or MAT1-2), or homothallic “mating” (self), which occurs between two cells of the same individual that have (in most cases) both types of mating genes (MAT1-1;MAT1-2). Previous studies have demonstrated that in the genus Cochliobolus, a MAT gene isolated from the homothallic species C. luttrellii can confer homothallism on a MAT-deleted strain of the heterothallic species C. heterostrophus. The objective of this study was to test if the MAT genes isolated from the heterothallic C. heterostrophus can convert the homothallic C. luttrellii to heterothallism. We expressed, separately, the heterothallic C. heterostrophus MAT1-1-1 and MAT1-2-1 genes in the MAT-deleted C. luttrellii strain by co-transformation. Analysis of the transgenic C. luttrellii strains revealed that: 1) A C. luttrellii transgenic strain carrying C. heterostrophus MAT1-1-1 and a C. luttrellii transgenic strain carrying C. heterostrophus MAT1-2-1 can mate in a heterothallic manner and the fertility of the cross is similar to that of a wild type C. luttrellii self, suggesting that a homothallic strain can be made heterothallic by exchange of MAT genes. 2) A C. luttrellii transgenic strain carrying ChetMAT1-1-1 can mate with the parental wild type C. luttrellii MAT1-1;MAT1-2 strain, indicating the latter is able to outcross, a result which was expected but has not been demonstrated previously. 3) A C. luttrellii transgenic strain carrying C. heterostrophus MAT1-2-1 cannot mate with the parental wild type C. luttrellii MAT1-1;MAT1-2 strain, indicating outcrossing specificity. 4) Each transgenic C. luttrellii strain carrying only a single C. heterostrophus MAT gene is also able to self, although the fertility is low, suggesting that both MAT1-1-1 and MAT1-2-1 genes of C. heterostrophus carry equivalent transcription regulatory activities, each capable of promoting sexual development when alone, in a suitable genetic background. The data presented in this study support the argument that in Cochliobolus spp., the primary determinant of reproductive mode is MAT itself. The methods developed may be applicable to other homothallic ascomycete plant pathogens for which, “heterothallic” strains can be generated by genetic manipulation of the MAT locus so that segregating populations can be obtained to facilitate genetic analysis of pathogen-host interactions.

Technical Abstract: Sexual fungi can be self-sterile (heterothallic, requiring genetically distinct partners) or selffertile (homothallic, no partner required). In most ascomycetes, a single mating type locus (MAT) controls the ability to reproduce sexually. In the genus Cochliobolus, all heterothallic species have either MAT1-1 or MAT1-2 (but never both) in different individuals whereas all homothallic species carry both MAT1-1 and MAT1-2 in the same nucleus of an individual. It has been demonstrated, previously, that a MAT gene from homothallic Cochliobolus luttrellii can confer self-mating ability on a mat-deleted strain of its heterothallic relative, Cochliobolus heterostrophus. In this reciprocal study, we expressed, separately, the heterothallic C. heterostrophus MAT1-1-1 and MAT1-2-1 genes in a mat-deleted homothallic C. luttrellii strain and asked if this converts homothallic C. luttrellii to heterothallism. We report that: 1) A C. luttrellii transgenic strain carrying C. heterostrophus MAT1-1-1 and a C. luttrellii transgenic strain carrying C. heterostrophus MAT1-2-1 can mate in a heterothallic manner and the fertility of the cross is similar to that of a wild type C. luttrellii self. Full tetrads are always found. 2) A C. luttrellii transgenic strain carrying C. heterostrophus MAT1-1-1 can mate with the parental wild type C. luttrellii MAT1-1;MAT1-2 strain, indicating the latter is able to outcross, a result which was expected but has not been demonstrated previously. 3) A C. luttrellii transgenic strain carrying C. heterostrophus MAT1-2-1 cannot mate with the parental wild type C. luttrellii MAT1-1;MAT1-2 strain, indicating outcrossing specificity. 4) Each transgenic C. luttrellii strain, carrying only a single C. heterostrophus MAT gene, is able to self, although all pseudothecia produced are smaller than those of wild type and fertility is low (about 4-15% of the number of wild type asci). These data support the argument that in Cochliobolus spp., the primary determinant of reproductive mode is MAT itself, and that a heterothallic strain can be made homothallic or a homothallic strain can be made heterothallic by exchange of MAT genes. The selfing ability of transgenic C. luttrellii strains also suggests that both MAT1-1-1 and MAT1-2-1 genes of C. heterostrophus carry equivalent transcription regulatory activities, each capable of promoting sexual development when alone, in a suitable genetic background.