Interplanting with legumes

Technique Overcoming Sterility
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1

I have read that nitrogen fixing bacteria have the capacity to infect some plant roots and, via nucleic plasmids, transfer symbiotic enchancing genes into the recipient. Here is an example:

Abstract The symbiotic plasmid (pSym1-32) of the highly effective Rhizobium leguminosarumbv. viceae1-32 strain was identified after the conjugal transfer of replicons carrying Tn5-mobinto the plasmidless Agrobacterium tumefaciensGm1-9023 strain. Plasmid pSym1-32 was transferred intoR. leguminosarumbv. viceaestrains Y14 (showing low effectiveness of symbiosis with Vicia villosa) and Y57 (unable to fix nitrogen). Transconjugants formed Fix+nodules on roots of V. villosaand had a highly enhanced nitrogen fixing ability, increased plant weight, and increased nitrogen accumulation compared to the recipient strains. Variation of transconjugants in symbiotic properties (accompanied by alterations in plasmid composition in some of the conjugants) was detected. Moreover, the donor strain R. leguminosarumbv. viceae1-32 was shown to be more efficient in the competitiveness and acid tolerance than the recipient Y14 strain. Both these properties were transmitted upon transfer of pSym1-32 into the recipient. Thus, plasmid pSym1-32 was shown to carry genes involved in the control of the nitrogen fixing ability, symbiotic effectiveness, competitiveness, and acid tolerance in R. leguminosarumbv. viceae.

O. N. Kurchak

Email: genet@riam.spb.su

N. A. Provorov

Email: genet@riam.spb.su

B. V. Simarov

Email: genet@riam.spb.su

http://www.springerlink.com/content/w210265361863322/

The relevance to rose breeding is the potential to create low fertilizer requirements in roses, which would likely have a significant market impact. Although the success probability is low, rose breeders are known for their patience, eg. sorting through 10,000 seedlings in the hopes of finding a handful of slightly improved varieties.

My suggestion is an experiment to interplant roses with a variety of short leguminous plants (clover, alfalfa, non climbing peas and beans, …) to infect the roots with several leguminous plasmid genes. Bacteria are extremely adaptable given time. If the roses are left unfertilized, they may be receptive to the benefits of at least partial symbiosis.

Any Rosarian possessing genetics laboratory equipment could transfer the plasmids without the need of infection, possibly accelerating the process.

2

I do not think this paper indicates any hope of creating roses capable of fixing nitrogen. In this paper they were only altering the bacterial side of the plant-bacteria symbiosis. The plant was completely unaltered, and already able to form symbiotic relationships with nitrogen fixing bacteria. The bacteria was just altered to be more effective at fixing nitrogen. For roses to be able to form symbiotic relationships with nitrogen fixing bacteria, the rose genome would have to be extensively altered. There has been interest in attempting such a transformation in major crop plants like corn, but to my knowledge, no one has been successful yet. Even if it was accomplished experimentally in a laboratory, the regulations regarding genetically engineered organisms are so strict it is highly unlikely such a plant would ever actually reach the market.

3

It is my understanding that many plants have some of the genes necessary for symbiosis, possibly from ancient relationships. Roses however, have not come up in my reading, so their standing is unknown to me. An important question is, are the genes needed by the plant for symbiosis found in the nitrogen fixing bacteria, specifically in the plasmids that readily transfer genetic content to other organisms. If so, then encouraging infection by proximity (mechanical injury may help) of innumerable bacteria would have the potential to succeed. I realize the chances are very small. If it happens in the field it is nature, if it happens in a laboratory it is genetic engineering :slight_smile:

4

you are getting into a very big field here. Dupont spent millions and gave up. A number of companies came and went. My post-doctoral advisor got into the national academy of sciences for his work speculating on how to make corn fix nitrogen and more practically, understanding how bacteria do fix nitrogen. The genes are probably too many to fit on an ordinary plasmid. Agrobacterium transfers DNA directly into the plant chromosome so in principle it could do something that might be stable but again the amount of DNA that would have to move is probably too much. What really works against it though is that the enzymes for nitrogen fixation are very sensitive to oxygen and plants require a lot of oxygen. so the root nodules made on legumes have special mechanisms to protect the bacteria from oxygen. that’s the genes that are present in many plants besides legumes.

Species closer to roses do have actinomycetes that make nodules on their roots. Examples are Russian olive, Ceanothus, Eleagnus, Myrica, Alnus and others less well known. There are bacteria that live in sugarcane in very poor soils and help them some, without making nodules.

I suspect that you’d never get nitrogen fixation to happen in plants grown on the high fertility soils required for ordinary roses. Even legumes regulate their nitrogen-fixing activity so that they don’t do unnecessary work. In rich soil they fix no N, on poor soil they fix all they need. Very efficient strategy for tehm but not particularly helpful for us.

Still, interplanting with legumes is a good idea if you mow down the legumes and use them for fertilizer, don’t add excess nitrogen to the soil in chemical form, and provide enough other nutrients and water so there isn’t too much competition between the legumes and the roses.

5

The below paragraph speaks of symbiotic fungi in grass, but if Dupont wants corn, the solution appears to be to inject bacteria into the corn stalk of a stressed corn plant and let the bacteria infect the seed themselves. Sounds too simple. The legal issues would deter me.

“These endophytes are transferred from plant to plant via seed. The mycelium of the fungus then grows into the sheath, stem, and leaf tissues of the developing grass seedling and maturing plant. Finally, the fungal endophyte enters the flowering stem and seed. The endophyte is passed to the next generation of turfgrass plants through the seed.”

http://www.uri.edu/ce/factsheets/sheets/endophyte.html

I was able to find a member of the rose family Rosaceae that already can fix nitrogen, complete with nodules. It is called Bitterbrush, Purshia tridentata. Found in the arid western U.S.

http://www.usask.ca/agriculture/plantsci/classes/range/purshia.html

The roots of nitrogen fixing plants extrude flavonoids, and similar substances, which attract the needed bacteria, so liquefying Purshia tridentata roots and using it as a root drench for the target, a nitrogen starved and stressed plant, would be a way of getting the target to accept a chronic infection of, in this case, Frankia bacteria. Once successful, perennial fruiting crops (with it’s symbiont from a close relative), or roses, could then be reproduced asexually with this characteristic intact.

“Addition of the flavonoids quercetin and diadzein to the growth medium increased the extent of endophytic colonization of the conjugant in rice seedlings by colonizing throughout the plant. Population and in planta nitrogenase activity of Serratia in rice seedlings were significantly increased by addition of flavonoids, quercetin and diadzein, whereas growth hormones, IAA and NAA reduced the efficiency of Serratia. The inoculation of Serratia sp. with flavonoids increased the plant biomass and biochemical constituents of rice seedlings under controlled condition.”

http://www.springerlink.com/content/68310226jm607204/

I have to say I am a hobbyist, not a scientist, so I could be wildly off base here, but it does seem possible to me that given time the bacteria will make the adjustments needed.