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Re: hosta-open DIGEST V1 #483


I appreciate your joining us.  We need some geneticists among us (I am
including you Ben).  I think, however, that we could all use a simple
explanation of transposable elements with an example such as seed color in
corn.  I fear we are beginning to float way over everyone's head.  I have
often wondered if Hosta variegation could at least be partially explained by
transposable elements.  I have figured that in our lab we see a new
variegation in something less than 10,000 individuals, which is clearly not
a simple mutation process.  I think we need to get terminology straight
before any arguments proceed.  Is the movement of an element a mutation or
is there a better way to describe this?  What is a position effect?

Ben thinks that H. Patriot -- Minuteman and probably other wide margined
thick leaf 'sports' are tetraploids not some other type of change.  I admit,
that I would be more comfortable with a chromosome count, but Ben's
techniques should show ploidy.

I would like to see a simple explanation of how you think the transposable
elements are involved in streaking.  And, especially in Hosta such as
Revolution, Allegan Fog, and our Fuzzy (all fortunei from what I can see)?
How about the net type variegations of Strip Tease, Spilt Milk, and Winter
Lightning?  I would also invite Ben to give his explanation (or at least
some speculation) for these phenomena, as clearly we have a difference in
opinion here.

Jim Anderson

-----Original Message-----
From: halinar@open.org <halinar@open.org>
To: hosta-open@mallorn.com <hosta-open@mallorn.com>
Date: Tuesday, August 10, 1999 2:24 AM
Subject: Re: hosta-open DIGEST V1 #483

>>Jim Anderson had asked a question (number 1) regarding
>>similarities/differences between variegation in daylilies and
>>hostas. I had declined to participate in this question because of my
>>limited familiarity in daylilies.
>There are very few variegated daylilies and they are mostly unstable.
>A variegated seedling will show up from time to time, but they tend to
>be mericlinal chimeras and few form a stable periclinal chimera.
>>I summarized the concepts defined by Jones(1934) wherein chimeras
>>(multicolored adjacent tissues) are a result of mutations within
>>specific cells which create two or more colors within cells and
>>subsequent, corresponding tissues.
>I think hosta people need to get away from thinking in terms of
>mutations as the cause of variegation in hostas and start looking at
>the problem from a logical point of view.  First, I don't know of any
>other plant genera like hosta.  Hostas are NOT mutating at any higher
>rate then any other plants.  When you look at any other plant genera
>you don't see the level of variegation that you see in hosta.  If
>hosta variegation was due to mutations then you would see the same
>level of mutations in other plants.  I know the Great Ben proposes
>mutations as one cause of hosta variegation and sporting, but Ben
>doesn't know much about botany.
>Secondly, if you propagate enough hostas you see that certain types
>keep reappearing.
>Variegation in hostas is most likely due to either transposable
>elements or some other mechanism that turns genes on and off.
>Some time ago I gave Ben a clue to figuring this out, but apparently
>he doesn't know enough about higher plants and apparently doesn't have
>the observational skills to figure this out, besides not knowing how
>to propagate hostas.  If you look at Francee in the spring you see
>that the margins are lighly yellow when the new leaf is still small.
>If you look at Patriot you see that the edges of new leaves are
>yellow, but a deeper yellow.  The leaves of Patriot have a wider edge,
>the color of the center is a darker green and if you feel the leaves
>they have a thicker, heavier feel to them.  If you propagate enough
>Francee you see this Patriot form showing up from time to time, but
>sometimes not as intense as Patriot.  Also, you get light green forms
>from time to time.  This is a POSITION effect.  I'm amazed that the
>Great Ben couldn't figure this out, especially considering he is
>suppose to be knowledgeable about fruit flies where position effects
>were first studied.
>This spring I had five sports out of Whirlwind from 7 plants.  Three
>of the sports had leaves that were folded in half with a narrow white
>center.  After the 4-5th leaf the new leaves started getting flater,
>but still with a thin center.  Now the newest leaves are pretty much
>like Whirlwind.  All three plants that had this initial type of leaf
>did this gradual change.  This behavior is not due to mutations.
>In cats calaco coloring is due to turning off of one of the X
>chromosomes.  Some cells have the paternal X on while other cells have
>the maternal X on.  When the X chromosomes get turned on/off
>determines the calaco pattern you see.  Streaked hostas are the calaco
>cats of the hosta genus, except it's not a X/y based sex chromosome.
>In a two layer histogenic structure the corpus (L2) doesn't have the
>organized apical initials like the L1 layer does.  Therefor, the cells
>in the L2 apex can be a mosaic pattern of genes that are turned on or
>off, or a position effect through a transposable element - this would
>result in a streaked hosta.  A streaked hosta would revert to a
>"stable" edged/center variegation pattern when the cells in the apex
>of the L2 layer all revert to having the transposable element at the
>same location.  A edged/center hosta can revert to a streaked form
>when some of the transposable elements shift position resulting in a
>mosaic pattern in the L2 apex.
>Getting a good understanding of transposable elements is difficult.
>Genetics textbooks in the 60's and 70's don't discuss them because
>they were not understood well at the time, and by the 80's and 90's
>genetics textbools were being written from a biochemical and molecular
>biology point of view and also mostly ignore transposable elements.
>For those who might want to do some searching of the literature,
>search for articles by Barbara McClintock.
>Now, I wonder how long it will be before I see this showing up in the
>Hosta Journal as Ben's latest theory on variegation in hostas.  I
>certainly hope he will give me some credit!
>Joe Halinar
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