W9 Prac questions Flashcards
In wild typischen Arabidopsis Blüten sind die Sepalen, Petalen, Stamina und
Karpelle in verschiedenen Wirteln angeordnet. Sie finden eine mutante Blüte, die nur aus Sepalen und Petalen besteht. Wie könnte dieser Phänotyp basieren auf dem ABC Modell erklärt werden?
The ABC model of flower development states that different combinations of activities of the three classes of homeotic genes specify organ identity in flowers. ‚A‘ class genes (AP1, AP2) specify sepals in the first whorl. ‚B‘ class genes (AP3, PI) in combination with ‚A‘ specify petals in the second whorl. ‘B’ in combination with ‘C’ specify carpels in the third whorl, and the class ‚C‘ gene (AG) alone
specifies stamens in the fourth whorl. In addition, ‚A‘ and ‚C‘ class genes act
antagonistically, preventing each others expression in the opposite whorls. If a
mutant flower contains only petals and sepals, it is most likely lacking agamous (a ‚C‘ gene) function. Consequently, ‚A‘ class genes (AP1, AP2) expand their expression domains into whorls 3 and 4 where they specify sepals and petals as in whorl 1 and 2. In addition, the meristem becomes indeterminate, producing
repetitions of whorls 1 and 2, which leads to a high number of petals. Interestingly,
roses and other ornamental flowers are often ‚C‘ class mutants, explaining their
beautiful flowers.
Arabidopsis Planzen, welche das LEAFY Gen unter der Kontrolle des konstitutiven
35S-Promotors exprimiert wird, zeigen normale Blütenmorphologie. Wieso? Welche anderen Phänotypen könnten mit der Überexpression von LEAFY assoziiert sein?
LEAFY, a meristem identity gene, together with APETALA1 and CAULIFLOWER,
controls the transition to flowering. Since LEAFY is expressed in early floral
primordia long before the flower homeotic genes are expressed, additional LEAVY
resulting from a 35S:LFY transgene (constitutive and ubiquitous over-expression) does not interfere with floral organ identity, and the flowers are normal. However, in critical tissues where LEAFY is normally not expressed, 35S:LFY causes a gain-of-function LEAVY phenotype, including an accelerated transition to flowering, and transformation of lateral vegetative meristems into floral meristems.
Das AGAMOUS Protein hat fünf verschiedene Domänen. Wie stehen diese
Domänen in Bezug zur Funktion von AGAMOUS, und wie würden Sie testen,
welche Domänen für die Funktion notwendig sind?
Sequence analysis of the AGAMOUS protein suggests it acts as a MADS-box
transcription factor: it activates transcription of target genes upon binding to their
cis-regulatory DNA. The minimal requirement for a transcriptional activator are a DNA-binding and a transactivation domain. From the N to the C terminus, five
domains can be identified in AGAMOUS: the N domain, the M or MADS-box
region (suspected DNA-binding domain), the K domain (similar to keratin protein in
animals), the intervening I region, and the C or carboxy terminal region. A series of
chimeric proteins that combine the different subdomains of AGAMOUS with a
known DNA-binding domain, and a corresponding cis-regulatory sequence that
controls expression of a reporter gene, allow testing for transactivation activity using reporter assays in cellular systems. To identify the DNA-binding activity (we assume the DNA-binding motif of AGAMOUS is known), systematically expressing chimeric proteins that each harbor a specific AGAMOUS subdomain and a welldefined transactivation domain could be used to explore which subdomain of AGAMOUS can bind to cis-regulatory sequence of the reporter gene, and
subsequently induce expression of the reporter gene via the known transactivation
domain. Alternatively or in addition, gelshift assays can be envisaged. In such an
experiment, various AGAMOUS subdomains would be tested for their ability to cause retention of labeled target DNA sequence in the gel. The proposed
experiments could provide the information which subdomains are sufficient for
transactivation and DNA-binding. In a next step, AGAMOUS proteins with
deletions in previously defined regions could be tested find out whether the deleted
residues are not only suffcient, but also necessary for AGAMOUS function.
LEUNIG kontrolliert die Expression von homeotischen Genen: Es reprimiert
AGAMOUS Transkription in Wirteln 1 und 2. Was für einen Phänotyp haben leunig
Mutanten? Haben Sie eine Idee, wie man einen leunig Phänotyp auf andere Weise
erreichen könnte?
LEUNIG (LUG) has cadastral function: its only role seems to inhibit the expression
of AGAMOUS in whorls 1 and 2. Unlike the ABC homeotic genes, LUG has no
instructive role to specify organ identity. lug mutants have organ identity
transformations in whorls 1 and 2, consistent with ectopic expression of AG in
whorls 1 and 2.
Sie haben eine Arabidopsis Pflanze erhalten, in der die Funktion aller homeotischen Blütengene defekt ist. Wie sieht diese Pflanze aus, und was würden Sie aus diesem
Phänotyp schliessen?
Flowers in this plant are abnormal: all floral organs appear as leaves. This might
suggest that leaves are organs produced in the absence of a specific signal (‚default‘
or ‚ground state‘), while flower organs represent modified leaves.
Eine neue Publikation beschreibt eine Tripelmutante, in der die drei SEPALATA
Gene (SEP1, SEP2, SEP3) mutiert sind; Einzelmutanten haben einen wildtyp
Phänotyp. Die Blüten bestehen ausschliesslich aus Sepalen. Wie erklären Sie sich diesen Phänotyp und was können Sie daraus über die SEP Gene aussagen?
The sepalata triple mutant resembles b,c-function deficient plants: petals, stamens
and carpels are not produced. Therefore, SEPALATA genes seem to be required for B,
C-genes to exert their function.
