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New receptor involved in symbiosis between legumes and nitrogen-fixing rhizobia identified

Legumes are able to grow in nitrogen-poor soils due to their ability to engage in symbiosis with nitrogen-fixing bacteria. There is a great interest in using the knowledge about this symbiosis, to enable transfer to other non-symbiotic plants. An international research team has come a step further to understanding this complex biological process. Microbes, whether beneficial or harmful, play an important role in all organisms, including plants. The ability to monitor the surrounding microbes is therefore crucial for plant survival. For example, the roots of a soil-growing plant are surrounded by a microbial-rich environment and have therefore evolved sophisticated surveillance mechanisms.

Unlike most other plants, legumes, such as beans, peas or lentils, are capable of growing in nitrogen-poor soils with the help of microbes. In a process called root nodule symbiosis, legumes form a new organ called the nodule where specific soil bacteria, called rhizobia are hosted. Inside the nodule, rhizobia convert atmospheric nitrogen into ammonium that is provided to the plant increasing growth. The legume in turn, supplies the bacteria with carbon resources enabling their energetically demanding nitrogen-fixing process.

The interaction between the legume plants and rhizobial bacteria is very selective. Previous research has shown that plants are able to identify specific signaling molecules produced by the symbiotic rhizobial bacteria. In particular one recognition system, called the Nod factor signaling, is crucial for establishing the host-nonhost relationship between legumes and rhizobia.

In order to initiate the symbiosis, the legumes use specific receptor proteins that can recognize the Nod factor molecules produced by bacteria. Two Nod factor receptors, NFR1 and NFR5, are well-known. They belong to a large family of so-called LysM receptor kinase proteins, which suggests that other similar receptors may be involved in Nod factor signaling as well.

An international research team of researchers from Denmark, Italy, France and Japan has now identified the role of another LysM receptor kinase called NRFe by studying a model legume species, Lotus japonicus. The results showed that NFRe and NFR1 share similar and distinct biochemical and molecular properties. NRFe is expressed primarily in the cells located in a specific area on the surface of the roots. Compared to NFR1, NFRe has a restricted signaling capacity restricted to the outer root cell layer. When NRFe was mutated, less Nod factor signalling was activated inside the root and fewer nodules formed.

NFR1-type receptors have also been found in plants outside the family of legumes, which do not form a symbiotic relationship with rhizobial bacteria. Identifying receptors important for Nod-factor signaling could provide a basis for new biotechnological targets in non-symbiotic crops, to improve their growth in nutrient-poor conditions.

Read the paper: Epidermal LysM receptor ensures robust symbiotic signalling in Lotus japonicus.

Article source: Aarhus University.


Plant mothers 'talk' to their embryos via the hormone auxin

While pregnancy in humans and seed development in plants look very different, parallels exist -- not least that the embryo develops in close connection with the mother. In animals, a whole network of signals from the mother is known to influence embryo development. In plants, it has been clear for a while that maternal signals regulate embryo development. However, the signal itself was unknown -- until now. Plant scientists at the Institute of Science and Technology Austria (IST Austria), Central European Institute of Technology (CEITEC) and the University of Freiburg have now found that a plant hormone, called auxin, from the mother is one of the signals that pattern the plant embryo. Their study is published in Nature Plants.

Archaeologists discover bread that predates agriculture by 4,000 years

At an archaeological site in northeastern Jordan, researchers have discovered the charred remains of a flatbread baked by hunter-gatherers 14,400 years ago. It is the oldest direct evidence of bread found to date, predating the advent of agriculture by at least 4,000 years. The findings suggest that bread production based on wild cereals may have encouraged hunter-gatherers to cultivate cereals, and thus contributed to the agricultural revolution in the Neolithic period.

Climate change-induced march of treelines halted by unsuitable soils

New research from the University of Guelph is dispelling a commonly held assumption about climate change and its impact on forests in Canada and abroad.