Researchers at Nanyang Technological University, Singapore, have re-engineered a plant's immune receptors into a more effective arrangement, and report that the best arrangement is four.
The work, published in Science Advances, used synthetic protein engineering to reorganise flagellin sensing 2, or FLS2, a receptor that detects flagellin, a protein associated with bacteria.
FLS2 does not work alone. It operates alongside partner receptors, and the NTU team set out to establish which combination produced the strongest response.
Two FLS2 receptors paired with two partner receptors gave the best result. Engineered plants showed approximately 53% less bacterial growth than unmodified controls.
The plants also grew normally. Immune responses are metabolically expensive, and a common failure in this field is a plant that defends itself thoroughly at the cost of everything else it was supposed to do.
Receptor stoichiometry — how many copies of a protein sit together in a working complex — was the variable the team set out to control. Rather than adding receptors indiscriminately, they engineered defined combinations and compared the responses each one produced.
The tests used Arabidopsis thaliana, a laboratory model plant from the same family as chye sim and kai lan.
Arabidopsis is used because it is small, fast and thoroughly mapped, and because results found in it often transfer to crops in the same family. The 53% figure is a laboratory result in a laboratory plant, and NTU presents it as one.
NTU described the approach in plain terms. “Our method is similar to putting more guards at a watchtower. Having the right number makes it easier to spot an intruder and respond quickly, but having too many can get in the way.”
The study was led by Professor Miao Yansong with Research Fellow Dr Wang Jinge. Two technologies arising from the work have been filed for patent through NTUitive, the university's innovation company.
The watchtower comparison is the team's own, and it should be taken at its word, because it settles a staffing question that has been open since the invention of the watchtower.
The optimal complement is four. Not three, which is understaffed. Not five, which gets in the way. Four.
This is, so far as the Department of Unnecessary Research can establish, the first published establishment figure for an organism that cannot convene a meeting to agree one. The plant did not negotiate it. The plant was issued with it.
The implications for the tower are considerable. A fifth guard reduces the effectiveness of the other four, which means that in cellular terms recruitment beyond the establishment is not merely wasteful but actively adverse — a conclusion most organisations have had to arrive at the long way round.
Performance under the approved complement is a 53% reduction in intruders. The guards work continuously, take no leave, and cost the plant nothing measurable in growth.
Arabidopsis thaliana therefore operates at full establishment, with a vacancy rate of zero and no procedure for appointing a fifth guard. On the published figures it is the best-run structure in Singapore.