Karyn,

So these are from the same plant? So *possibly* this could represented two different bud sports on the same plant...so *maybe* the plant could be somehow prone to bud sports? That would make sense, if a particular plant had increased rates of transposition, for example. And surely someone knows something about this--but my guess would be that bud sports formed by a transpositional mechanism would be less stable than those due to point mutations. Again that's IF this is due to two bud sports on separate regions of the plant AND the mechanism is increased transposition.

This does sound like a strange plant! Save as many pieces as you can.

I don't remember much about genetics but is transposition where a sequence of the DNA moves to a different spot on the gene whereas a point mutation is a change in a base nucleotide? What's the difference in the effect each has on a plant. In layman's terms please. lol

In any case just the one branch has the white blooms. There's been flowers on pretty much the whole plant and all have been normal except the one branch. I was able to get almost the whole plant moved intact. It took over an hour to untangle the vines but I really wanted to give the fruit a chance to ripen. As soon as it's ripe I'll take cuttings and try to root them. I'm just pleased that I was able to get the plant in without having to cut the fruit off.

Hi Karyn,

Great to hear about the plant and the white bloom/lighter fruit part. I am curious whether the large fruit is also reproducible on the other part of the vine.

You're exactly right about the transposition vs. point mutation difference. The deal is that with some forms of transposition it is in principle reversible--the DNA segment that has inserted itself into another region of DNA can pop right out again.

In principle there may be no difference between a defect caused by a tranposition event and a point mutation. One example: lets say a gene of interest codes for an enyzyme necessary for making pigments. A point mutation may lead to a stop codon, for example, so that a shorter, inactive enzyme is made.

Similarly, the transposon could disrupt the enzyme gene in the middle of its DNA sequence by inserting foreign sequence. The foreign DNA sequence would itself lead to a shortened protein soon enough when by chance a stop codon were encountered. The end result could be a portion of the protein with a stretch of foreign amino acids added at a point corresponding to the site of transposon insertion*. The net result is the same--a truncated, inactive protein.

However, the chance that the point mutation leading to the truncation will be reversed is small--you'd have to hope for another mutation in the same point in the DNA correcting the first change. However, for certain types of transposons, the "foreign" DNA could just remove itself and insert elswhere, regenerating a functional enzyme. In principle it could be reversible.

So in the Passionflower there are enzyme(s) responsible for a transposition event itself--a "transposase". There are factors that keep this reaction in check--otherwise transposons would be popping in and out of genes at rates that would be hazardous for the plant. I don't know what these factors are, but there may, for example, be a protein that binds to the "transposase" enzyme, turning it off. Or maybe other proteins bind to the transposon DNA itself, blocking the transposase from cutting it out as might be needed for a transpositional effect. Regardless, the easiest way of getting a transposon with an increased rate of transposition would be to weaken or inactivate (presumably by a mutation) these proteins that keep the reaction in check.

Anyway, under such a scenario--which should be possible at least in principle--you could generate a plant with increased tendency towards bud sports. And if it's the reversible sort of transposition I would expect they might revert with some frequency. That may or may not be the case.

If the large fruit is persistent on that part of the vine (maybe you already know) it would be intriguing if there were more than one bud sport. Regardless, the question of whether your white flower is stable or not may depend on the source of the mutation, and if it's a transposon whether it's reversible or not. I would think if the lack of pigmentation was caused by a point mutation the change would be quite stable.

By the way, I grabbed a quick Wikipedia reference below--I didn't realize that the corn (maize) genome is 50% transposons. Humans, I believe, are something like 20%. It's hard to think of it as "foreign" DNA.

*since there are 64 codons and 3 of these are stop codons, by chance in random sequence this might happen after about 20 random amino acids are added on. The sequence might not be random, though...

Here is a link that might be useful: Wikipedia transposon article