If crop science continues to advance at the pace it has over the last two decades, we hope secure, sustainable and affordable food could be only a further decade away.

This is according to a research review by scientists at the Crop Science Centre, which has summarised the last ten years of dramatic advances on the topic of how legumes use beneficial microbial associations to fulfil their need for nutrients.

Lead author Dr Min-Yao Jhu from the Crop Science Centre said, “Our current food production systems are unsustainable, driven in part through the application of chemically fixed nitrogen fertiliser, which is environmentally damaging and prohibitively expensive for some small-holder farmers. We need alternatives to maximise crop yields in an equitable and environmentally sustainable way. By highlighting our understanding of legume nodulation and the unsolved mysteries in the field, we hope this review can provide a road map for upcoming research to overcome the barrier of achieving self-fertilising crops.”

Ten years of scientific advances have provided researchers with detailed frameworks for understanding the processes involved in legumes fixing their own nitrogen. Some examples include: how legumes recognise nitrogen-fixing rhizobia, how rhizobia infect legume roots, the development of nodules on legume roots, and how legumes create an environment appropriate for nitrogen fixation.

One key discovery highlighted by the review is that symbiosis signalling is not limited to legumes. Our target cereal crops have inherited processes involved in forming symbiosis with arbuscular mycorrhizal fungi, which appears to be the evolutionarily earliest beneficial microbial association in plants. This symbiosis signalling shares many similarities with the signalling pathway for recognition of nitrogen-fixing rhizobia in legumes. What does appear to have changed is the strictness of signal recognition through the receptor complex; legumes have an exacting perception of signals produced by the rhizobia with which they form a symbiotic relationship. Discoveries such as these mean that scientists can develop self-fertilising cereal crops by re-networking pre-existing processes, rather than creating new ones from scratch. Importantly, this is a realistic challenge for the next decade, assuming the pace of scientific advancement remains the same as it has done over the last twenty years.

A further scientific breakthrough highlighted by the review is that the processes involved in forming symbiosis between legume plants and rhizobia bacteria are principally controlled by a few key master regulators. Therefore, the authors recommend studying how these master regulators activate the regulatory networks needed for nodule development in different cell types. Answering this question will require using emergent spatial-omics techniques, such as single-cell sequencing and spatial transcriptomics, to examine the developmental processes associated with nodulation with a high degree of cellular resolution.

Author of the paper and director of the Crop Science Centre, Professor Giles Oldroyd, said “Two decades of discovery science in model legumes have laid the foundations of our understanding to do something truly radical: transfer the ability of N-fixation to a much broader range of crops.  I am excited about the potential this brings for sustainable and equitable food production and I strive to get there within my research career.”

This review forms part of The Engineering the Nitrogen Symbiosis for Africa (ENSA) research programme, which utilises natural symbioses between plants, soil fungi and bacteria to engineer crops to make better use of nutrients already present in the air and the soil. This would allow sustainable increases in crop yields, potentially revolutionising smallholder farming in low-and-middle-income-countries, while providing a viable solution to sustainable and secure food production in high-income countries.

Here is a link to the review paper Dancing to a different tune, can we switch from chemical to biological nitrogen fixation for sustainable food security? | PLOS Biology

A microscopy suite opened in December of 2022 has enhanced the Crop Science Centre’s research capabilities.

This new facility offers confocal microscopy, which enhances the study of the symbioses dynamics between plants and beneficial microorganisms, including fungi and bacteria. In addition, the suite provides systems for imaging of calcium oscillations in plant roots, which enables Microscopy Specialist and Crop Science Centre researcher Dr Jongho Sun, to conduct research onsite that is key to engineering self-fertilising cereal crops.

Dr Susana Sauret-Gueto, Crop Science Centre Research Services Manager and Microscopy Specialist, manages the Microscopy Suite and led the acquisition of a confocal microscope, and responded to the opening of the suite by saying “It is fascinating to see researchers new to confocal microscopy, straight away adding an extra dimension to confocal experiments by using both fluorescence intensity and fluorescence lifetime-based information in their experiments”.

Experienced microscopist and researcher at the Crop Science Centre, Dr Jen McGaley, said “The Stellaris [confocal microscope] has massively increased the resolution and depth to which we can explore the dynamics of mycorrhizal fungi within plant roots. The fluorescence lifetime imaging capacity provides confidence in what we are imaging, and having plant growth and microscopy facilities under the same roof has opened the doors to visualising processes in live plant-fungal symbioses.”

The suite is still growing, with systems to support sectioning and screening of samples soon to be added.

A Cambridge-led consortium has received US$35m (£28m) over five years to develop sustainable solutions to increasing the yields of small-scale farmers in sub-Saharan Africa, without the need for costly and polluting inorganic fertilisers.

The grant, from Bill & Melinda Gates Agricultural Innovations (Gates Ag One), will enable researchers led by the University of Cambridge Crop Science Centre to engineer plants to take advantage of naturally occurring interactions with micro-organisms – fungi and bacteria – that help in the uptake of nutrients from the soil and air.

“African agriculture is at an inflection point, with vastly increasing demand at a time when supply is at risk, especially due to a changing climate,” said Giles Oldroyd, Director of the Crop Science Centre and Russell R Geiger Professor of Crop Science.

“The outcomes of this work have the potential to see gains as great as those from the Green Revolution, but without relying on costly and polluting inorganic fertilisers.

“Increasing sustainable production of crops in small-holder farming systems, like those in sub-Saharan Africa, directly addresses some of the worst poverty on the planet.”

Nutrients are vital to the success of crops. However, the land of small-scale farmers in sub-Saharan Africa is depleted of nutrients. Artificial fertilisers are too expensive for small-scale farmers to buy, and their livestock numbers too low to produce sufficient levels of manure to nourish their crops. This leads to deceasing yields overtime, which affects livelihoods. Average maize productivity in sub-Saharan Africa is less than a quarter of that in the USA.

The Engineering the Nitrogen Symbiosis for Africa (ENSA) research programme utilises natural symbioses between plants, soil fungi and bacteria, that deliver nutrients to the plant. By leveraging these relationships ENSA aims to engineer crops to make better use of nutrients already present in the air and the soil. This would allow sustainable increases in crop yields, potentially revolutionising smallholder farming in low-and-middle-income-countries, while providing a viable solution to sustainable and secure food production in high-income countries.

The grant funds the Engineering the Nitrogen Symbiosis for Africa (ENSA) research programme. ENSA is a Cambridge-led international collaboration with partners: University of Oxford, UK; NIAB, UK; Royal Holloway University of London, UK; Aarhus University, Denmark; Wageningen University and Research, The Netherlands; University of Freiburg, Germany; University of Toulouse III Paul Sabatier, France; University of Illinois, USA; Pennsylvania State University, USA.

A not-for-profit subsidiary of the Bill & Melinda Gates Foundation, Gates Ag One was created to leverage global crop science to meet the needs of smallholder farmers in sub-Saharan Africa and South Asia. It focuses on accelerating research that enhances the biological processes of six priority food crops: cassava, cowpea, maize, rice, sorghum, and soybean.

“The pioneering work of ENSA is fundamental to levelling the playing field for smallholder farmers in Africa, leveraging the latest crop technology to ensure all communities have the chance to thrive,” said Joe Cornelius, CEO of Gates Ag One. “Breakthrough advances in crop science and innovation mean intractable challenges like nutrient uptake and soil health need not hold back agricultural development. We’re delighted that Gates Ag One can support ENSA to continue its work to meet the needs of smallholder farmers.”

A research review by a Crop Science Centre scientist and a UC Davis scientist has summarised our current understanding of how the stem parasitic plants Cuscuta species, known as dodders, develop the specialised organs, called haustoria, which confer the ability to acquire water and nutrients from their host plants.

Lead author, Dr Min-Yao Jhu at the Crop Science Centre, said, “This review not only reveals the fascinating mystery of how plants evolved parasitism, but also provides the foundation for developing more effective methods to control the agricultural damage caused by parasitic plants.” 

Parasitic plants are notorious for causing billions of USD worth of agricultural losses globally each year. Progress has been made recently in understanding the evolution and development of haustoria in root parasitic plants. Yet, increasing studies indicate that behaviours of haustorium formation between root and stem parasites are distinct, and the formation mechanisms of these organs in stem parasitic plants remain largely unknown.

Interestingly, although most root parasitic plants can avoid attacking themselves or closely related species, this does not appear to be the case with dodders.

This review also outlines the advantages of using dodders as model organisms for studying haustorium development in stem holoparasitic plants, the mysteries and limitations in the dodder system, and potential future research directions to overcome these challenges.

Frontiers | Cuscuta species: Model organisms for haustorium development in stem holoparasitic plants (frontiersin.org)

Research by Crop Science Centre scientists’ sheds light on the relationship between arbuscular mycorrhizal fungi and lateral root development in angiosperms.

Professor Uta Paszkowski, an author of this research, said “This is a significant clarification of the molecular mechanisms triggering cell division, thereby underpinning crop root system architectural plasticity in the ecosystem. This forms an important part in our wider ambition to improve the nutrition of crops sustainably.”

Published in the journal Current Biology, this research has four key findings: the initiation of new lateral root primordia, generic chitin as a potent stimulus of lateral root development, conserved MAMP receptors to perceive the chitin signals and the broadly conserved response across diverse angiosperms.

The ability of arbuscular mycorrhizal fungi to increase lateral root numbers in various plant species has been widely observed. This research reveals that the cause is increased initiation of cell division and lateral root primordia formation.

This enhanced lateral root development was thought to be activated by symbiosis relevant signals, such as LCOs or CO4. However, the authors of this research clarify that lateral root development is generic to diverse chitin-derived molecules. Furthermore, the authors present genetic evidence demonstrating a conserved lateral root developmental response to chitinaceous molecules across phylogenetically distant angiosperms, involving a dedicated set of MAMP receptors.

In a broader ecological and evolutionary context, the exact biological significance of this conserved response requires more investigation. The authors speculate that the detection process of chitinaceous molecules might facilitate the monitoring of the soil biota.

This pre-existing signalling pathway might be an ancestral feature of all plants engaging in nitrogen-fixing symbioses where diazotroph bacteria also employ chitinaceous LCOs to stimulate cell-division leading to nodule formation. This finding is therefore important for potential engineering of nitrogen fixation into cereal crops.

This research forms part of a wider programme to improve the sustainability of equity of global agriculture by reducing the need for inorganic fertilizer. This will be particularly beneficial for small-holder farmers in sub-Saharan Africa who do not have access to inorganic fertilisers to increase the yield of their crops.

Read the research in Current Biology by following this link Arbuscular mycorrhizal fungi induce lateral root development in angiosperms via a conserved set of MAMP receptors - ScienceDirect