Genetic mutations that mildly decrease mitochondrial function have been shown to markedly increase lifespan. In exploring the molecular mechanisms responsible for the increase in lifespan, it was shown that knocking down the expression of UBL-5, a ubiquituin-like protein that is required for the mitochondrial unfolded protein response (mitoUPR), reverts the long lifespan of the
clk-1 and
isp-1 mitochondrial mutants to WT (Durieux et al., 2011). It was subsequently demonstrated that knocking down the expression of ATFS-1, a transcription factor that acts with UBL-5 to mediate the mitoUPR, does not affect the longevity of
isp-1 worms (Bennett et al., 2013). Thus, the role of the mitoUPR in mitochondrial mutant longevity remains unclear. In this work, we confirm that the mitoUPR is activated in
clk-1,
isp-1 and
nuo-6 mitochondrial mutants during development and throughout adulthood. To examine the role of the mitoUPR in the longevity of these mutants, we crossed these worms to an
atfs-1 deletion mutant (
gk3094). We found that only the
nuo-6;
atfs-1 double mutants are viable and fertile, while
isp-1;
atfs-1 double mutants and the progeny of
clk-1;
atfs-1 double mutants fail to develop to adulthood. Similarly, when
clk-1 and
isp-1 worms are grown on
atfs-1 RNAi from the parental L4 stage, the progeny do not develop to adulthood. Accordingly, we measured the lifespan of
clk-1,
isp-1 and
nuo-6 worms on
atfs-1 RNAi beginning at the experimental L4 generation. Under this paradigm, we found that
atfs-1 is not required for the lifespan of any of these mutants. In contrast, we found that knocking down
atfs-1 beginning in the parental L4 generation decreases the lifespan of
nuo-6 worms, while an
atfs-1 mutation completely reverts
nuo-6 lifespan to wild-type. Combined these results demonstrate that ATFS-1 is required for the long lifespan of
nuo-6 worms and suggest that its effect on lifespan occurs during development. In characterizing the
nuo-6;
atfs-1 double mutants, we have identified multiple genes involved in stress resistance that exhibit an
atfs-1-dependent increase in expression in
nuo-6 worms. We are currently studying which of these changes in gene expression contribute to the longevity of
nuo-6 mutants. Overall, this work suggests that the ability to activate the mitoUPR during development is crucial for the survival and lifespan of long-lived mitochondrial mutants.