GRAVITROPIC GENE EXPRESSION DIVERGENCE ASSOCIATED WITH ADAPTATION TO
CONTRASTING ENVIRONMENTS IN AN AUSTRALIAN WILDFLOWER
Abstract
Plants adapt to their local environment through complex interactions
between genes, gene networks, and hormones. Although the impact of gene
expression on trait regulation and evolution has been recognized for
many decades, its role in the evolution of adaptation is still a subject
of intense exploration. We used a Multi-parent Advanced Generation
Inter-Cross (MAGIC) population, which we derived from crossing multiple
parents from two distinct coastal ecotypes of an Australia wildflower,
Senecio lautus. We focused on studying the contrasting gravitropic
behaviors of these ecotypes, which have evolved independently multiple
times and show strong responses to natural selection in field
experiments, emphasizing the role of natural selection in their
evolution. Here, we investigated how gene expression differences have
contributed to the adaptive evolution of gravitropism. We studied gene
expression in 600 pools at five time points (30, 60, 120, 240, and 480
minutes) after rotating half of the pools 90°. We found 428 genes with
differential expression in response to the 90° rotation treatment. Of
these, 81 genes (~19%) have predicted functions related
to the plant hormones auxin and ethylene, which are crucial for the
gravitropic response. By combining insights from Arabidopsis mutant
studies and analyzing our gene networks, we propose a preliminary model
to explain the differences in gravitropism between ecotypes. This model
suggests that the differences arise from changes in the transport and
availability of the hormones auxin and ethylene. Our findings indicate
that the genetic basis of adaptation involves interconnected signaling
pathways that work together to give rise to new ecotypes.