Crops like maize, rice and wheat are economically of high importance, however current
yield will not sustain the world’s demands in the long run. Plant roots are crucial for
uptake and transport of minerals, hormones and water via their vasculature and are
therefore of interest for yield improvement. Unfortunately, root development is not yet
completely understood and the research that has been performed to date has mainly
focused on the dicotyledon (dicot) model system Arabidopsis thaliana (Arabidopsis).
Dicots differ substantially from most crops, the majority of which are monocotyledons
(monocots). for which Brachypodium distachyon (Brachypodium) was recently proposed
as a good model system. It is closely related to wheat and barley, and more distantly to
rice, with a smaller genome and simplified growth conditions that make it suitable for
research. My thesis has therefore focused on transferring knowledge from Arabidopsis
root development into Brachypodium in order to determine to what degree research in
dicots can be applied to monocot root development. The first gene that I studied was
AUX1 which is coding for an auxin importer. Mutations in Arabidopsis AUX1 only resulted
in mild root phenotypes whereas in monocots, including Brachypodium, the phenotypes
also include shoot dwarfism and even sterility. Furthermore Brachypodium aux1 mutant
displays increased root cell elongation and reduced cell diameter. Other genes that were
further investigated during this thesis are OCTOPUS (OPS), BREVIS RADIX (BRX),
CLAVATA3/EMBRYO SURROUNDING REGION 45, BARELY ANY MERISTEM 3 and
BRASSINOSTEROID INSENSITIVE 1. All of them affect protophloem development in
Arabidopsis and mutations in OPS and BRX result in small roots due to undifferentiated
cells within the protophloem. In order to analyze these gene families in Brachypodium, we
developed a CRISPR-Cas9 genome editing system to create the corresponding mutants.
We discovered that most Brachypodium homologs were part of bigger gene families and
therefore multiple members may have to be mutated in order to observe putative
phenotypes. This project is still ongoing, however preliminary data suggests that indeed
for BRX family members, single, double and triple mutants do not induce phenotypes.
Also preliminary results for double ops family member mutants, indicate the lack of root
phenotypes. As for AUX1, these preliminary results differ from the phenotypes observed
in Arabidopsis and underlines the importance of research in a monocot model plant in
order to understand crop development better and hopefully improve yield on the long
term.