The Telomerase Reverse Transcriptase Subunit from the Dimorphic Fungus Ustilago maydis

Abstract

In this study, we investigated the reverse transcriptase subunit of telomerase in the dimorphic fungus Ustilago maydis. This protein (Trt1) contains 1371 amino acids and all of the characteristic TERT motifs. Mutants created by disrupting trt1 had senescent traits, such as delayed growth, low replicative potential, and reduced survival, that were reminiscent of the traits observed in est2 budding yeast mutants. Telomerase activity was observed in wild-type fungus sporidia but not those of the disruption mutant. The introduction of a self-replicating plasmid expressing Trt1 into the mutant strain restored growth proficiency and replicative potential. Analyses of trt1 crosses in planta suggested that Trt1 is necessary for teliospore formation in homozygous disrupted diploids and that telomerase is haploinsufficient in heterozygous diploids. Additionally, terminal restriction fragment analysis in the progeny hinted at alternative survival mechanisms similar to those of budding yeast.

Contributions of recombination and repair proteins to telomere maintenance in telomerase‐positive and negative Ustilago maydis

“…maydis trt1 deletion causes progressive telomere loss and the emergence of type I-like survivors Because we are interested in understanding the roles of repair proteins in both telomerase-positive and telomerasenegative cells, we first characterized the U. maydis telomerase-null mutant. Bautista-Espana et al recently reported the identification of U. maydis Trt1 (the catalytic subunit of telomerase), and demonstrated telomere loss and the emergence of survivors in the trt1D mutants (Bautista-Espana et al, 2014). Notably, most of the TRF (telomere restriction fragment) analysis in this study was conducted using a sub-telomeric probe, making it difficult to compare the findings to typical assays that employ the telomere repeat probe.…”

“…Bautista‐Espana et al . recently reported the identification of U. maydis Trt1 (the catalytic subunit of telomerase), and demonstrated telomere loss and the emergence of survivors in the trt1Δ mutants (Bautista‐Espana et al ., ). Notably, most of the TRF (telomere restriction fragment) analysis in this study was conducted using a sub‐telomeric probe, making it difficult to compare the findings to typical assays that employ the telomere repeat probe.…”

“…S1B). Notably, Bautista-Espana et al had also observed in their survivors a 350 bp, PstI-generated fragment that annealed to subtelomeric probes (Bautista-Espana et al, 2014). The amplification of a restriction fragment that hybridizes to telomere and subtelomeric probes is characteristic of a class of S. cerevisiae (budding yeast) telomerase-null cells known as type I survivors.…”

Mre11 and Blm-Dependent Formation of ALT-Like Telomeres in Ku-Deficient Ustilago maydis

“…maydis ku mutants, we analyzed several independent trt1 ku70 nar1 double mutants, which were constructed by first deleting the trt1 gene (encoding the telomerase reverse transcriptase in U . maydis [ 28 ]) and then introducing the ku70 nar1 allele. Similar to the ku70 nar1 single mutant, the double mutant experienced growth arrest when switched to the restrictive condition for ku70 expression ( Fig 3A and 3B ), and exhibited profound telomere aberrations ( Fig 3C, 3D and 3E ).…”

Telomere recombination pathways: tales of several unhappy marriages

“…Also, unlike budding yeast but similar to fission yeast, U. maydis has a mammal-like telomere nucleoprotein complex (Yu, et al 2013). Notably, initial analysis of the U. maydis telomerase-null mutant trt1 Δ did not reveal an ALT-like pathway, but rather survivors that resemble the S. cerevisiae type I survivors ((Bautista-Espana, et al 2014) and E.Y.Y., unpublished data). Instead, the Ustilago ALT-like pathway was discovered in the course of investigating Ku function.…”