My current research at The University of Adelaide and the Waite Research Institute involves understanding how the mycorrhizal pathway of Zn uptake functions – a problem I began working on during my PhD. Although we have a fundamental understanding of how plants acquire phosphate (Pi) via symbiosis with mycorrhizal fungi, very little research has been conducted to uncover the mechanisms (genes, transporters) that underlie the transport of Zn from fungi to plant, presumably across the peri-arbuscular membrane. We have shown through radioisotope tracking that plants can acquire Zn via the mycorrhizal pathway (see below), so the next step will be to uncover the genes that regulate this process. To do this, I am using barley as a model plant species, due to its relevance to Australian agriculture. In some experiments I also use Medicago truncatula, an important pasture legume in Australia. I work in collaboration with, and am housed within the labs and greenhouses of: A/Prof Tim Cavagnaro – a soil ecologist, and Prof Steve Tyerman – a plant physiologist.
My previous work in Prof Maria Harrison’s lab involved characterising variation in plant physiological responses to formation of arbuscular mycorrhizas in the important and diverse cereal crop Sorghum bicolor. I did this by using the parent lines of a NAM population. These 15 parent lines are designed to represent the huge diversity in morphological and physiological characteristics apparent in sorghum. By growing these diverse lines of sorghum with different AM fungi, and measuring a range of physiological responses such as plant yield and tissue nutrient concentrations, we can start to identify where the potential lies for the mycorrhizal symbiosis to improve the quality of sorghum. I also used Brachypodium distachyon, a model plant species for sorghum and other grasses, to dissect and describe the genetic basis of mycorrhizal phosphate (P) and ammonium uptake, using CRISPR/Cas9 molecular cloning techniques. You can read an article in the Cornell Chronicle on this research here.
During my postgraduate research at Monash University, I studied how the mycorrhizal symbiosis can improve plant zinc (Zn) nutrition, and how this is in turn affected by the phosphorus concentration of the soil. Tomato was my study species, and I had a mutant genotype (named rmc: reduced mycorrhizal colonisation) that was unable to be colonised by mycorrhizal fungi. When compared to its wild-type progenitor, 76R, the rmc plants provide an excellent non-mycorrhizal control for glasshouse experiments. The exciting thing about AM is that they play two very different roles in improving plant Zn nutrition. On Zn-deficient soils, AM deliver extra Zn to the plant to increase its tissue Zn concentrations. However, on a soil contaminated by heavy metals, plants colonised by mycorrhizal fungi are actually afforded ‘protection’ from the excess Zn in the soil. By studying this three-way AM*Zn*P interaction, I discovered that the ability of AM to improve plant Zn nutrition is dependent upon soil P concentration, which is highly relevant to agriculture where phosphate fertiliser is often liberally applied to the soil. I have several papers covering this research: 1, 2, 3.
While spending time at the Technical University of Denmark under the supervision of Prof Iver Jakobsen, I undertook a number of experiments using radioactive isotopes of P (33P and 32P) to trace P acquired by mycorrhizal fungi from the soil and transferred to the plant. Using a combination of split-root pots, isotope labelling and a Medicago truncatula genotype mutated in MtPT4 (the AM-inducible phosphate transporter gene in Medicago), we concluded that the long-distance impact of AM colonisation on the direct pathway of phosphate uptake (via root hairs) is limited. Want to read about it?
During a research visit to the University of Adelaide, I used a radioactive isotope of Zn (65Zn) to trace the uptake of soil Zn via the mycorrhizal pathway, into plant shoots. By doing this, I quantified for the first time the actual amount of Zn that is contributed via the mycorrhizal pathway compared to the direct pathway. Read about here!
In the future I would like to work on improving our knowledge of how AM can enhance plant Zn nutrition by combining the knowledge we have on plant physiological responses to AM with the characterisation of plant Zn transporters, and along with cutting-edge molecular biology techniques, use this to dissect the molecular mechanisms behind AM-mediated improvements in plant Zn nutrition. Stay tuned…