The Government has set a target to plant 10,000 hectares of trees per year in England by 2025. However producing enough trees to meet this demand requires faster propagation techniques. Tree cutting propagation depends on root formation from stem bases, however there is significant variation in rooting success between species. This variation is dependent on signalling networks including plant hormones such as auxin which is the core ingredient of many rooting powders. However auxin treatments do not always improve rooting on difficult-to-root species, partly due to increases in auxin degradation. In this project the student will identify whether auxin responses and degradation previously discovered by the primary supervisor can be applied to industry-relevant cuttings of Cornus species (edible and biodiversity value) while developing a novel method for targeted delivery of auxin. By adding auxin to the right cells at the right time for root initiation we can overcome low-auxin-related blocks to rooting.
This PhD will combine plant physiology experiments with pharmaceutical solutions for hormone delivery to cuttings at the right time to optimise cutting propagation for a commercially relevant output. Objective 1: Identify if auxin responses previously discovered in model systems also apply to Cornus cuttings. Building on Rasmussen et al 2015, auxin levels and responsiveness will be measured in harder to propagate Cornus cuttings collected from Whetman Plants International. Grafting will be used to confirm if the signal is shoot or root-derived. Auxin, cytokinins, strigolactones and jasmonic acid levels will be measured in the rooting zone to compare to our pea model. Laser Ablation Tomography will be used to track root initiation and emergence processes in 3D. Objective 2: Develop pharmaceutical carriers for novel auxin delivery to manipulate local auxin at key times post-cutting The student will synthesise nanocarriers to deliver auxin and auxin metabolites in a spatially and temporally targeted manner.
This will involve producing (bio)polymer-based capsules (e.g., PLGA, PCL, chitin, chitosan) trapping Auxin inside. These will be fed to the cut end of DR5:GUS lines of Pea which will provide a marker to demonstrate auxin release. They will then be fed to commercial Cornus sp. cuttings to test the impact on root formation compared to alternative protocols including cotton feeding, microinjection, microdialysis delivery and mixed in lanolin. Objective 3: Interference with auxin movement and metabolism to improve rooting The auxins IBA, 2-4-D and NAA are more stable with different mobility to IAA and will be applied with and without NPA (auxin transport inhibitor) to cuttings along with the three most effective polyphenols for stabilising auxin (ferulic acid, caffeic acid and vanillin). For each of these compounds PsDR5:GUS will be used to observe changes in auxin response parallel to rooting response in Cornus sp.
Funding is available for four years from late September 2022. The award covers tuition fee (£4,567) at the home rate plus an annual stipend (£15,840) for 2022. This is set by the Research Councils. UK and international candidates are eligible to apply.