in some zones of mexico brassica rapa persist as a weed, however, etnical groups use it as food for in early stages of development or for feed birds. i think the answer is related with the management or its association with others.

Consider this site:

https://www.arabidopsis.org/portals/education/aboutarabidopsis.jsp

"What is the record for a shorter life cycle reported in Arabidopsis?"

Did you mean in natural status? Otherwise, remember that a life cycle of Arabidopsis (or other plants) can be reduced or extended artificially by applying different environment cues, or by genetically transformation.

Thank you very much for your answers, Gerardo, Enezio and Yuan-Yeu.

The point is that in the site indicated by Enezio I don't see the information requested in the question, i.e.: What is the record for a shorter life cycle reported in Arabidopsis?

Five weeks? Four?

Of course the cycle can be reduced by genetic and environmental cues. But the questions are :

1. What is the shortest time reported to accomplish the full cycle (seed to seed)?

2. Is this related with a particular physiological (internal) condition, for example auxin imbalance?

Hi Emilio,

1. Not so sure about the record short life-cycle of Arabidopsis plant.

2. As you said, the Wisconsin fast plants (WFT, Brassica rapa) are the product of a breeding program developed for decades. Through years of artificial selection, the 'favorable alleles' for 'fast growth' are selected in the current progeny. Therefore, the 'fast growth' phenotype can be attributed to these favorable alleles which might have different plant functions, and not just only one.

For example, the UPBEAT1 (UPB1)-like gene can be one of these alleles. UPB1 controls the gene expression of enzymes known as peroxidases. These peroxidases control the balance of free radicals between the zone of cell proliferation and the zone of cell elongation where differentiation begins. When the researchers experimentally disrupted UPB1 activity in the plant root, it altered the balance of free radicals such that cells delayed their differentiation and continued growing (In "Gene Discovery Suggests Way to Speed Plant Growth").[ https://today.duke.edu/2010/11/growfast.html ]

@ Yuan-Yeu,

I think that selection of fast-cycling plants took much more than 15 years and was done mainly by the Nature. RC Brassica rapa was selected from original Nepal landrace with a little longer life cycle. I worked with both original (flower after 5th true leaf) and CrGC1 (flower after 3rd true leaf) plants. My former boss, Dr. Kenichi Hida said that CrGC1 must have generative organs tissue formed in seeds already.

See for RC plants origin: 

http://fastplants.org/about/the_story_of_fast_plants.php

@Emilio, RC Brassica rapa stands alone - it has very stable fast life cycle, other RC brassicas are more depended on environmental condition for flowering. In 1sq cm pot they are fast, in large pot - rather slow.

But, if you take several hundreds seeds of almost any spring brassica variety (rape, mustard), put them in small soil volume (+ expose seedlings to low temperature) you may find several plants that flower almost like CrGC fast plants.

@ Alex,

Yes, the origin of those plants already showed fast-growing phenotype before their seeds were brought to the US, then University of Wisconsin-Madison. Dr. Paul Williams then performed artificially selections on them for many years, including select for those plants flowered the fastest. Those plants are then dubbed as 'Wisconsin Fast Plant' (WFP). I think they also registered this name, and use it as FAST PLANTS®. I remember that when I was at UW-Madison, we used WFP in Genetics class. Nowadays, if you go to ASPB (American Society of Plant Biologist) annual conference, you still can see them setting up a stand for handing out free seeds and handout for educators. A few years ago, they were doing some mapping, but I did not follow-up their projects. Thank you for reminding me that.

 @Yuan-Yeu, it is interesting that my colleague has found in Pamir (part of Himalaya system) barley landrace with fastest life cycle among all known accessions. I guess that specific climate + UV radiation may increase natural selection for fast seed production.   

@ Alex,

I am interested in the RC Brassica rapa. I have a few questions:

1. What is 'RC' stands for? (Edit: Rapid Cycling, I found the answer)

2. When you say 'RC Brassica rapa', did you refer to WFP?

3. "RC Brassica rapa was selected from original Nepal landrace with a little longer life cycle."  Will 'longer life cycle' contribute to a somewhat larger vegetative mass?

4. By the way, actually they already published mapping results from WFP (mapping which I mentioned above) (see attachment), but mainly for teaching purpose.

@ Yuan-Yeu,

The names were changing... When I started to work, it was called CrGC 1 (B. rapa), later Rapid Cycling Br, now - WFP. I am not sure that they are identical, after all - this is cross-pollinating population, and it must be changing in time. Longer life cycle of Nepal landrace was linked to larger plant size. But, CrGC1 flowering time  was not so depending on soil volume as FT of other RC plants.

Actually, I would try to develop RC plants from self-pollinating yellow sarson or Hiroshimana, or from easy-double haploiding pet-sai cultivars. Sarson was used in mapping work, and it would be easier to find genes for fast life cycle in its progeny. I like an idea of my colleagues from HRI - Wellesbourne - they have used CrGC3 (B. oleracea) to cross to hard-flowering wild Brassica n=9 complex accessions, and made mapped DH lines from F1 hybrids, easy crossing to commercial B. oleracea plants.    

Emilio, Woo HH, Faull KF, Hirsch AM, Hawes MC. in the work "Altered life cycle in Arabidopsis plants expressing PsUGT1, a UDP-glucuronosyltransferase-encoding gene from pea. Plant Physiol. 2003 Oct;133(2):538-48" have described 4-6 weeks cycle of Arabidopsis plants - 2 weeks faster comparing to original plants.

Thank you very much Alex. This is the kind of reference I was looking for. Now a question is ¿Do these mutant plants complete the cycle in water-agar or do they need more nutrients?

It is also interesting that the transgenic plants contain an UDP-glucuronosyltransferase. I suppose it alters cell wall formation, thus probably accelerating cell cycle in general. ¿Don't you think so?

Will check the article. Thank you

UDP glycosyltransferases mediate the transfer of glycosyl residues from activated nucleotide sugars to acceptor molecules (aglycones), thus regulating properties of the acceptors such as their bioactivity, solubility and transport within the cell and throughout the organism. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC138907/

In the reference paper they used Murashige and Skoog

medium. Transgenic plants were under maintained in a controlled environmental chamber with 16 h of light (mixed fluorescent bulbs) at 21°C and 8 h of dark at 19°C and were carried through five generations before analysis of phenotype.

It was not mentioned that they used soil of water agar for plant growth.

@ Alex,

About your earlier statement, "my colleague has found in Pamir (part of Himalaya system) barley landrace with fastest life cycle among all known accessions. I guess that specific climate + UV radiation may increase natural selection for fast seed production."   

There is a hypothesis called 'evolutionary-rates hypothesis". The evolutionary-rates hypothesis suggests that high environmental energy availability elevates rates of molecular evolution, promoting faster speciation. And evidence supports that high levels of ultraviolet radiation increase mutation rates (see attached paper #1).

So, it is very likely. The other evidence is that researchers have found dwarfism Arabidopsis (due to GA gene mutation) on two geographically proximal high-altitude sites in the Alps, which was not found in 855 other Arabidopsis strains (see the attachments #2 and #3).

However, they did not link 'generation time' to the hypothesis.

@ Emilio (and Alex),

For your question: "............the transgenic plants contain an UDP-glucuronosyltransferase. I suppose it alters cell wall formation, thus probably accelerating cell cycle in general. Don't you think so?"

The authors of the same group who published the paper posted by Alex has provided some answers in their second paper (see attachment). It can be to do with 'flavonoids'. Read on....[ Cited from the Discussion section of their paper, see yellow highlights in the paper ].

"Several models are consistent with the observed effects of altered UGT expression in transgenic plants, and with the direct effects of flavonoids on root function. First, the removal of flavonoid aglycones in UGT ectopic expression mutants could influence regulatory enzymes such as kinases and phosphatases, which play key roles in cell cycle regulation. Flavonoids affect invasion and proliferation of tumor cells through direct or indirect control of the cell cycle. Although the details of their functions in plants are not known, flavonoids can act as internal physiological regulators or chemical messengers at relatively low levels. Flavonoids such as kaempferol function as auxin transport inhibitors."

Interesting that Thiamethoxam could be an antagonist of flavonoids as auxin transport inhibitors and, thus, stimulates plant growth and development (it was registered as Vigor(TM) effect). http://gcirc.org/fileadmin/documents/Proceedings/IRCWuhan2007vol4/258-261.pdf

Hello Alex, Results showed are in canola, do you think the effects can be clear in other crops? Thanks for your comments. Sergio