ABC(D) Model of Plant Flowers - (Dec/20/2014 )

Hello,

I think I understood the basic principles of the ABC-Model (for example that there are only Sepals and Carpels if there is a mutation in B function genes) but now I have to use this model to explain some mutations that I don't understand:

- "A mutant tomato developes fruits but has no sepals, instead petals in its first sector."

My thoughts about this: If it has fruits, it means that at least C (for carpels) works. It has no sepals, so there must be a mutation in genes for A. But I read that A and C are antagonists, so if there is no A, C takes its place which would result in Carpel, Stamina, Stamina, Carpel. So how can there be Carpels and Petals but no Sepals?

- "A mutant tomato can't develope carpels but can develop ovules."

How can that happen? I read that the ABCD model says that you need both, C and D for ovules!?

Can someone help me or knows a source where I can find out how this works? The articles I've read until now didn't help me with that.

Hello

I think this is more suited to the Plant biology forum but let me help you out. Added disclaimer: its been a while since I've worked on floral evolution and I've never worked on tomato.

You should be looking for articles on the ABCDE model as the ABC model is outdated. However, that actually doesn't sound right because you would expect carpels-petals-stamens-carpels because remember that the B-class genes are still functioning in A-class mutants. Sepals are only conferred by A-class genes so you would not expect sepals in A-class mutant flowers. Are you sure that the organs in the first whorl are not aborted so you get only whorls 2-4? That would explain why the first whorl are petals. Can you tell me which paper this is from?

Do you mean that A-class mutants can't develop ovules? You would expect carpels in A-class mutants because C- and E-class genes are still functioning. Ovules may not be present because A class genes do have a small function in the ovules (see Wikipedia for a short summary) which may explain why they are absent.  

As a side note always remember when you're reading about the ABC model that it is just a simplified (and very cool) representation of an very complex system. So results are never as defined as the model especially in species that are not Arabidopsis.