GET3B interacts genetically with components of the STIC pathway
(ALB4 and STIC2)
Previously we had shown the negative -synergistic effect of combining
the get3b and srp54 alleles (Anderson et al., 2021). A
functional interaction between the two factors also became apparent from
our proteomic analysis, in which get3b displayed a significant
enrichment of cpSRP substrates (Figure 1, supplemental table S1). This
could be due to a form of compensation for the absence or reduction of
GET3B function or the reduction of some stromal proteases which we could
also observe in the proteomic data (Supplemental table S1).
Additionally, the significant depletion of STIC2 in get3b prompted us to analyze the connection between the GET3B-, cpSRP- and the
STIC- components.
Hence, we utilized the existing single mutants srp54 (Amin et
al., 1999), stic2 (Bédard et al., 2017), alb4 (Gerdes et
al., 2006) and get3b , and double mutants srp54 get3b (Anderson et al., 2021), alb4 srp54, and alb4 stic2 (Bédard et al., 2017), and combined mutant alleles to create the double
mutants alb4 get3b and stic2 get3b , and triple mutantsalb4 stic2 get3b and alb4 srp54 get3b (Figure 4). To
assess the phenotypic consequences of these genetic combinations, we
measured the rosette diameter as an indicator of overall plant fitness.
Unlike the get3b , alb4 , stic2 single mutants andalb4 stic2 double mutant, the srp54 single mutant andalb4 get3b , stic2 get3b double mutants displayed a
significantly smaller rosette diameter compared to the wild-type (Figure
4A-F, H, I, M). Strikingly, this phenotypical trait was further
exacerbated in the srp54 get3b double mutant andalb4 stic2 get3b triple mutant (Figure 4G, J, M). These results
illustrate an additive or synergistic interaction between GET3B and STIC
components. Notably, the get3b allele in a srp54 background showed a more severe phenotype than in an alb4 stic2 background, suggesting a stronger functional interdependence between
GET3B and SRP54.
In order to better understand this interdependence as well as the effect
of the get3b allele on plant fitness, we analyzed the alb4
srp54 get3b triple mutant. While alb4 srp54 plants were smaller
than srp54 plants (Figure 4K, M), the addition of theget3b allele resulted in a further reduction in the measured
rosette diameter (Figure 4L, M). This demonstrated that the combination
of the alb4 , srp54 and get3b alleles resulted in an
additive detrimental effect on plant fitness.