Question
Auxins are plant hormones that coordinate several aspects of root growth and development. Indole-3-acetic acid (IAA) is an auxin that is usually synthesized from the amino acid tryptophan (Figure 1). Gene Trp-T encodes an enzyme that converts tryptophan to indole-3-pyruvic acid (I3PA), which is then converted to IAA by an enzyme encoded by the gene YUC.
(a) Circle ONE arrow that represents transcription on the template pathway. Identify the molecule that would be absent if enzyme YUC is nonfunctional.
(b) Predict how the deletion of one base pair in the fourth codon of the coding region of gene Trp-T would most likely affect the production of IAA.
Justify your prediction.
(c) Explain one feedback mechanism by which a cell could prevent production of too much IAA without limiting I3PA production.
(d) Rhizobacteria are a group of bacteria that live in nodules on plant roots. Rhizobacteria can produce IAA and convert atmospheric nitrogen into forms that can be used by plants. Plants release carbon-containing molecules into the nodules. Based on this information, identify the most likely ecological relationship between plants and rhizobacteria. Describe ONE advantage to the bacteria of producing IAA.
(e) A researcher removed a plant nodule and identified several “cheater” rhizobacteria that do not produce IAA or fix nitrogen. Describe the evolutionary advantage of being a bacterial cheater in a population composed predominantly of noncheater bacteria. Plants can adjust the amount of carbon-containing molecules released into nodules in response to the amount of nitrogen fixed in the nodule. Predict the change in the bacterial population that would cause the plant to reduce the amount of carbon-containing molecules provided to the nodule.
Answer/Explanation
Ans:
a) See diagram for circled arrow. If enzyme YUC is is non-functional, IAA will be absent.
b) The described deletion would likely significantly reduce IAA production. This is because deletion of a base pair in a gene often causes a frameshift, which alters all subsequent colors append different amino acids than intended, resulting in a Trp-T Enzyme that is non-functional due to a differ mg primary structure.
c) To limit IAA production without limiting I3PAproduction, a cell would need a negative feedback loop that presents Enzyme YUC avilabilability in the presence of excess IAA. An example could consist of epigenetic mulers produced in the presence of IAA that prevent transcription of the YUC gene, temporarily halting Enzyme YUC production.
d) The most likely ecological relationship between the plants & the mizobacteria is mutualism. An advantage for the bacteria producing IAA is that the host roots will grow & develop in the presence of the IAA auxin, expanding the bacteria’s habitat &ensuring the survival of the plant on which it depends.
e) Bacterial cheaters have an evolutionary advantage because they expend less energy on producing IAA & fixing nitrogen than non-cheters, giving them more energy to seek resources & reproduce and therefore increasingly their fitness. Due to this advantage, the bacterial population will exhibit a hire cheating frequency in subsequent generations. This results in less nitrogen fixation in the plant’s root nodules, which would cause the plant to reduce carbon compound releases in response.
a) The molecule that would be absent would be IAA
b) The deletion of one loase pair could lead to the enzyme Trp-T to not be produced properly or at all blc the deletion would affect the coding region of the gene, which would change the amino acid sequence, which would alter the protein that is produced after translation, IAA would not be produced blc the Enzyme Trp-T would not be usable or produced, so tryptophan can notIAA become I3PA which cannot be converted to IAA.
c) The cell could turn of the Gene YUC which would not create the Enzyme YUC which would mean I3PA could be converted to IAA.
d) The most likely ecological relationship between the two is mutualistic. Ore advantage of the bacteria producing the IAA is that it helps keep the plant developing and growing which gives the bacteria more shelter and better chance of survival than if the plant were dying.
e) The evaluation advantage of the bacteria that “cheat” is that they do not have to expand energy to help the plants and just survive off of the custom the plants give the bacteria this would give the “cheaters” more energy to reproduce instead of helping the plants grow. The change in the bacterial population would be one achieve the bacteria are producing an insufficient amount of IAA, so the plants are not benefiting off of the bacteria anymore.
a) The molecule that would be absent if enzyme YUC is nonfunctioning is indole-3-acetic acid (IAA).
b) The deletion of one base pair in the fourth codon of the coding region of gene Trp-T could stop the production of IAA. This is because a deletion of one base-pair can lead to a frameshift mutation, causing a different enzyme to probably be produced, if enzyme Trp-T is no longer produced by gene Trp-T, then I3PA cannot be made, which means nothing is available to be converted into IAA.
c) one feedback mechanism could be limiting the production of enzyme YUC. Without enough enzymes YUC, a lot of I3PA will not be able to be converted to IAA even if there are many of I3PA
d) Plants and Rhizobacteria most likely have a mutualistic relationship. one advantage of the bacteria producing IAA is that the IAA will coordinate aspects of root growth and development of the plant roots of the plant that the rhizobacteria live in.
e) The evolutionary advantage of being a bacterial cheater in a population composed of non-cheaters is that the cheater can have extra carbon intake but without doing work. The change in the bacteria population is that there will be more bacterial cheaters in the nodule.