Plant Growth and Development, BO/GN 733

Christina's questions 9/19/06 – Jaillais 2006   0.25in;" class="MsoNormal"> -[if" alt="" />supportLists]--> 1)       In figure 2, I don?t see much difference between n-p and q-s. 0.25in;" class="MsoNormal"> -[if"...

9/14/06 questions, Wildwater et al. Questions for Wildwater: 1) What exactly are "lox" recombination sites? 2) Their interpretation was that SCR has opposing effects in relation to RBR function and activity--what might this mechanism look like? 3) Where is the proximal meristem? ...

Wildwater-Qs In the scr-4, rBRr double mutant there's a restoration of the QC along with additional columella cells but there is no restoration of root size. I'm not sure how this is possible? I would guess that scr is also required for QC maintenance? In page 1342 top...

Questions for RBR Paper Question 1) In the model on page 1345 the authors show a pathway for RBR pathway action and interaction in plants, however I feel that this model is a bit premature, is there any other evidence in plant systems to support this model? Question 2) The...

RBR questions 9/12/06 ? Wildwater et al, Cell 2005 0.25in;"> userdefined="">  supportLists]--> 1)       After showing the reduced protein expression via western blot (fig.1K), couldn‘t the authors have fused GUS or ...

ok Looks like the blog is working for me as well. -Ramon

Plant Development Posting is Set Okay,  I guess I don't have an excuse for posting anymore!  I am on the list now! Cat

Lecture notes online now The link for the lecture notes is (and was) active. I hope everyone can now post new entries now; I have "invited" you and you should have received an email (unless I misspelled your email). I did not get a chance to talk about auxin and the paradox that...

Questions frm stds for Levesque questions for sept 10th 1) On page 744, the authors discuss the target validation for 4 out of the eight candidates. They describe expression patterns for SCR, MGP, NUC, but their is no evidence for TRI, is there? 2) What type of mutations are shr-2 and...

Control of flowering map This post is in regard to Bob's comments about the many ways that flowering is controlled in Arabidopsis. This is a late post because  it took me a while to figure out  how to  add a jpg. If anyone is missing a toolbar  above their text...

Gallagher - Q's frm students week two Qs from gallagher et al 1). they found that the SHR protein transloctates itself throughout the stele, and that pressumably, this occurs via plasmodesmata. I want to ask, how would you conduct a test to show that it does so? I am not ...

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.



 

Agamous and germ line specification Bob and I were talking after class about agamous and germ line specification. One of the major defects of expressing wuschel instead of (or in addition to) agamous is that no anthers or ovules are formed, as far as I could see. Developmentally, I think this means leaf-like structures can emerge (carpel primordia) but if no ovules are formed, agamous MAY have an additional critical function; to specify the germ line.

Just a bit of background... you can think of ferns as being similar to angiosperms (flowering plants) but they don't hide their seeds. Spores are found underneath the fronds. If you take the leaf-like frond and roll it up, like a pea pod, you have now hidden the seeds from view and created an angiosperm (means "hidden sperm"; gymnosperms have "naked sperm" where seeds lie on top of the cone scale, a modified leaf).

Sepals, petals, and carpels have the same "body plan" as leaves. Stamens are more specialized, but one could think of them as a midvein with a microsporoctye at the end (the anther).

What causes the switch to meiosis? Does agamous control that, or is the switch downstream of something specified by agamous? (Agamous would be epistatic to the switch.)

Even though carpel-like structures are formed in some of the mutants discussed in class, if they don't make seeds they are developmentally lacking in a very important process.

Welcome to Plant Growth and Development Hi! Both of your instructors are new to web blogs but we thought that they would be a great way to have a discussion about plants. So bear with us if we make mistakes. One of the first things I found out is that Safari (Macintosh) doesn't support posting. Firefox is great.

We'd like to hear from you about why you want to take this course, what kind of research you're doing, and anything else you'd like to tell us.
 

Here's my spiel: I'm really looking forward to learning about development and thinking about all the levels of regulation and interaction that are important for plant growth. Francis Collins (former head of the Human Genome Project) has a new book on his personal resolution of science and religion. What do you think of his idea that DNA can be thought of as scripture? Well, it's an interesting idea but I think RNA rules! Is there a master regulator? Or does everything work together? (I don't want to get into a discussion about religion, BTW, just wanted to get the ball rolling on some ideas!)

As you'll find out, Bob is a real geneticist and I'm a real plant person. I try to think like a geneticist but sometimes it's hard. I do bow before the awesome power of Arabidopsis genetics.

I do research on virus-induced gene silencing and also on transgenic methods for increasing ER calcium stores. I hope that some day this research will lead to more sustainable agriculture. I like the research because it never goes in a straight line and what you think will happen often doesn't. It's the challenge of re-thinking and then getting a clue that maybe you're on the right track that is really rewarding.

I have a 16 year old daughter who is learning to drive and who plays mellophone in marching band. My husband is director of the Plant Transformation Lab across the street from my lab. And we have a very sweet 9 year old German Shepard dog who likes sticks more than anything else in the world.

Looking forward to hearing from you!