Plant Growth and Development, BO/GN 733

Read and Respond - week one questions Below is a list of the questions that students turned in to me before the start of the last class.  I have added my comments in italics.  Please respond to some of these questions by blogging before our next class meeting.  I think you probably know some of the answers now that you might not have before the class.

Bob


1). If Wus is important to turn on Ag which would then terminate Wus function then why does the Wus mutant start the formation of a floral meristem at all?

I briefly went over this in class. WUS doesn?t actually start the floral meristem.  The meristem identity genes do this LFY is the main player, but AP1, and CAL are other players. A new meristem identity regulator, LMI1 has recently been identified see the possible student presentations document - check out the Saddic et al. 2006 Development 133, 1673-1682. LMI1 paper

Four pathways feed into turning on the meristem identity genes. These are day length, vernalization (a period of cold during the winter), Gibberillic acid pathways (a plant hormone) and an autonomous pathway that makes the plants more likely to flower as they get older. Thus environmental inputs can regulate when the vegetative meristem (that makes leaves) will convert to a /floral meristem that makes flowers.  Thus reproductive development can be timed so that it occurs at the right time of year and in the right environmental conditions.  Plants are so smart!!--

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2). If there is a limiting amount of AG necessary for termination of Wus then how would Wus expression only induce AG since AG would need to be on consistently after Wus expression was terminated to keep Wus inactive.

What else turns on AG? do you remember?

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3). How does Wus function both as a immortalizing factor (i.e. keeping the stem cells active) as well as a regulator of termination?

Good point: Can a protein have two dissimilar functions at two different developmental times? What are the molecular mechanisms for keeping stem cells active vs. for termination of stem cell population. Interesting that WUS (at least in part) is the trigger for both.


4) When ag mutants display interior flowers in the 4th whorl, are all 4 whorls reproduced in these flowers? (i.e. Whorl 1,2,3,1,2,3,...)?

answer is yes and basically indefinitely.

5) Why was it necessary to use the pOp/LhG4 two component system to connect the AG promoter to WUS expression?  Why not just create a true AG::WUS construct?

we went over this.

6) How do (can?) AG, WUS, CLV, LFY, AP, etc. be applied in the ABC floral gene model?  What other known components exist?

I touched on this again LFY and AP1 are major inputs to turn on the ABC genes initially.  Once on the ABC genes interact amongst themselves to refine their expression domains.


7) Why does stamen development in AG:WUS expressed plants have such a large variability?

This is a very tough question in general when plants give a variable phenotype.  We usually don?t know the exact answer, but I would like to hear some ideas from you all regarding what might account for variability in phenotype in this case and in general.

8) What is the trigger for WUS repression? A certain number of AG expressing cells forming?

Good question:  Can cells or promoters sense different concentrations of transcription factors?  If so how?

9) Regarding the in situ hybridization in Figure 1, the author mentions that it is difficult to quantify mRNA expression levels. Could they not have extracted mRNA at the different developmental floral stages and conducted quantitative RT-PCR for both WUS and AG expression levels (assuming the equipment is available)?

They could have but it might have been difficult to get enough tissue from the small young floral stages.  This can be done by laser microdissection a challenging technique even now, that was not readily available when this paper came out.

10) Wouldn?t it be beneficial to take a genomic approach also and see the expression of other novel genes by using a gene-chip, or high density, oligonucleotide-based DNA assay?  2b) After the novel genes are identified, they could proceed with the in situ hybridization expression patterns.

Can you expand on this idea.  What is the actually experiment.  What type of genomic approach?

11) Have any deletion assay of the AG promoter be done to determine what motifs are controlling the  repression activity? 3b) On the other hand, what motifs in the deleted WUS promoter control the expression of WUS.

This is definitely a valid approach. Analysis of the AG promoter has been done and has proven successful in identifying binging site for LFY and MADS-ox proteins. Less has been done on WUS promoter that I am aware of.