AGO1 and HSP90 buffer different genetic variants in Arabidopsis thaliana

Argonaute 1 (AGO1), the principal protein component of microRNA-mediated regulation, plays a key role in plant growth and development. AGO1 physically interacts with the chaperone HSP90 that buffers cryptic genetic variation in plants and animals. We sought to determine if genetic perturbation of AGO1 could also reveal cryptic genetic variation, and if so, whether AGO1-dependent loci would overlap with those dependent on Hsp90. To pursue these questions, we introgressed a hypomorphic mutant allele of AGO1 into a set of mapping lines derived from crosses of the commonly used Arabidopsis thaliana strains Col-0 and Ler. We found several instances in which this genetic perturbation buffered genetic variation; however, none of the AGO1-dependent loci overlapped with those buffered by HSP90 for the same traits. We focused on one buffered locus where AGO1 perturbation uncoupled the otherwise closely correlated traits days to flowering and rosette leaf number. Using a bulk segregant approach, we identified a non-functional Ler hua2 mutant allele as the causal AGO1-buffered polymorphism. Introduction of a non-functional hua2 allele in a Col-0 ago1 mutant background recapitulated the Ler-dependent ago1 phenotype, implying that coupling of these traits involves different molecular players in these closely related strains. Taken together, our findings demonstrate that even though AGO1 and HSP90 buffer genetic variation in the same traits, these robustness regulators interact epistatically with different genetic loci, suggesting that higher-level epistasis is uncommon. We also find evidence for rewiring of key regulatory pathways within the same species.

AGO1（Argonaute 1）作为介导微小RNA（microRNA）调控过程的核心蛋白组分，在植物生长发育中发挥关键作用。AGO1可与分子伴侣热休克蛋白90（HSP90）发生物理互作，该蛋白可缓冲动植物中的隐蔽遗传变异。本研究旨在探究AGO1的遗传扰动是否同样能够揭示隐蔽遗传变异，若可以，则AGO1依赖的遗传位点是否会与HSP90依赖的遗传位点存在重叠。为解答上述问题，我们将AGO1的低功能突变等位基因导入至由常用拟南芥（Arabidopsis thaliana）生态型Col-0与Ler杂交构建的作图群体中。研究发现，该遗传扰动可在多个案例中缓冲遗传变异；但针对相同性状而言，AGO1依赖的遗传位点与HSP90所缓冲的遗传位点并无重叠。我们重点关注了一个受AGO1扰动后可打破原本紧密关联性状（开花天数与莲座叶数）耦合关系的缓冲位点。通过集群分离分析方法，我们鉴定出一个功能丧失型Ler生态型hua2突变等位基因为受AGO1缓冲的因果多态位点。在Col-0背景的ago1突变体中导入功能丧失型hua2等位基因，可重现依赖Ler生态型的ago1突变体表型，这表明在这两个亲缘关系较近的拟南芥生态型中，上述性状的耦合过程涉及不同的分子调控因子。综合来看，本研究结果表明，尽管AGO1与HSP90均可对同一类性状的遗传变异起到缓冲作用，但这两类稳健性调控因子分别与不同的遗传位点发生上位性互作，这提示高层次上位性并不常见。此外，本研究还发现了同一物种内关键调控通路发生重布线的证据。