Flying the Flag for Photosynthesis

A lost Marine Biologist.

My transition from undergraduate to postgraduate study resulted in a move from counting anemonefish along sunny Indonesian reef flats to huddling under an umbrella, desperately cradling expensive equipment, in a rainy Cambridgeshire wheat field. This wondrous shift to researching on 'dry' land was motivated by my roots in agriculture and rising food security concerns, originally stemming from studying depleted fish stocks. So consequently, I sought out a practical exploration of food security at NIAB through my PhD, and it was there that I answered the call of the wild...wheat!

Two significant bottlenecks exist in raising bread wheat yields to meet increasing global demand. Firstly, the constriction of available genetic diversity through domestication and modern breeding techniques. Secondly, the difficulties in unlocking true photosynthetic potential throughout the growing season. These are important issues within the industry that I heard discussed during my first Monogram meeting in 2016. Fortunately, a potential avenue exists for addressing these concerns: wild emmer (AABB, Triticum dicoccoides) the tetraploid ancestor of bread wheat. Despite looking like a weed and being frustratingly troublesome to work with, wild emmer has already shown merit as a source for modern wheat improvement via disease resistance, drought tolerance and abiotic stress resilience.

 A wild emmer flag leaf cross section, used to correlate mesophyll conductance to anatomical features
A wild emmer flag leaf cross section, used to correlate mesophyll conductance to anatomical features.

Throughout my PhD, we have used infrared gas analyses in several field trials to identify wild emmer lines with superior photosynthetic flag leaf traits. Results showed that these wild emmer lines had accelerated rates of flag leaf photosynthesis, physiologically driven by enhanced characteristics which facilitate the supply of CO2 to the sites of carboxylation, such as high stomatal and mesophyll conductance. We found wild emmer lines had relatively small ears but long awns. However, they maintained higher CO2 assimilation per ear than modern wheat. This led to the investigation of how awns contribute to ear photosynthesis and if a potential trade-off exists with flag leaf carbon gain.

After exposing a series of desirable characteristics in the tetraploid background, we have started to dissect complex traits to piece together an ideal physiological flag leaf ideotype for a targeted environment. To map targeted traits, a novel tetraploid mapping population was created from two Triticum dicoccum lines which differed in photosynthetic strategies. QTL have been identified and mapped, in order to facilitate the introgression of desirable traits from a tetraploid background into hexaploid wheat. The ideotype could provide breeders with a physiological basis for selecting traits that improve photosynthesis. Designing the 'perfect flag leaf' involves aiming to keep some of the beneficial traits already present in modern wheat, such as leaf area and longevity whilst incorporating traits from wild emmer that would increase per unit area photosynthesis, for instance higher stomatal and mesophyll conductance

Publications showcasing this research are currently in the pipeline, which focus on QTL mapping in the T. dicoccum population, the significance of awn photosynthesis and a comparison of photosynthetic diversity in wild tetraploid and modern wheat. Overall, this has been a successful foray into the wild relatives of wheat as a source of genetic improvement, although it may only be a drop in the ocean of the plethora of potential diversity which still could be captured.

Tally Wright - Linkedin, Profile at Cambridge University - Profile at NIAB - Twitter@tallywright

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