Quantitative genetic analysis of auxin-driven growth in Arabidopsis Thaliana

Growth and development in plants displays genetic complexity differently controlled by
discrete environmental stimuli. The Arabidopsis thaliana hypocotyl is a useful model
system for studying growth due to its simplicity. The hypocotyl elongates in response to
a wide range of stimuli, including the phytohormone auxin. Auxin is a major regulator of
growth and development with a role in every stage of a plant’s life cycle. Previous work
has shown that exogenous auxin can increase hypocotyl length in some cases, but
decrease it in others. In this dissertation, I wanted to investigate the growth response to
auxin in two ways. I added exogenous auxin, and increased auxin levels naturally by
growing plants at warm temperatures. I also investigated the effect of the mutation
hsp90.2-3 on hypocotyl growth. This mutation increases hypocotyl length and reveals
cryptic genetic variation within a plant. I studied the effect of auxin and the mutation on
growth using a quantitative genetic approach.

I investigated growth using QTL analysis. This technique uses naturally occurring
variation in a population to detect regions of the genome which influence a certain trait.
It is useful for studying a trait like growth, which is controlled by many genes of small
effect. I detected many QTL using this technique, including one which has a role in
controlling growth and variation under several tested conditions. I also detected QTL
that work through epistatic interactions. Some QTL control a change in hypocotyl length
in response to a specific stimulus. Overall, I have studied the genetic basis of growth in
several conditions and examined the change in hypocotyl length and variation in
hypocotyl length due to changes in temperature and exogenous auxin. I envisage that
the genetic architecture I reported will aid future studies into the way warmth and
auxin affect growth and variation in plants.