The T-DNA region of the Ti plasmid of Agrobacterium tumefaciens harbours two genes: X and Y. Mutation of gene 'X' produces a rooty tumour while mutation of gene 'Y' produces shoots in the tumor. Based on the above information, which one of the following statements is correct?
Gene 'X' encodes cytokinins and gene 'Y' encodes auxins
Agrobacterium T-DNA Genes and Plant Hormones
The bacterium Agrobacterium tumefaciens causes crown gall disease in plants by transferring a segment of its tumor-inducing (Ti) plasmid, called the T-DNA, into the plant cell genome. This T-DNA carries genes that are expressed in the plant cell and manipulate its growth and development, leading to the formation of a tumor or gall.
Within the T-DNA region are genes responsible for the synthesis of plant hormones, primarily auxins and cytokinins. The balance between these two hormones plays a critical role in determining plant growth and differentiation. Specifically, the ratio of auxin to cytokinin controls the development of roots and shoots:
- A high ratio of auxin to cytokinin promotes root formation.
- A low ratio of auxin to cytokinin promotes shoot formation.
- An intermediate ratio typically leads to undifferentiated callus growth, which forms the basis of the tumor.
Analyzing T-DNA Gene X and Y Mutation Effects
The question states that the T-DNA harbours two genes, X and Y, and describes the results of their mutation:
- Mutation of gene 'X' produces a rooty tumour.
- Mutation of gene 'Y' produces shoots in the tumor.
Let's consider the implications of these mutation phenotypes based on the role of auxin and cytokinin ratios:
Mutation of Gene X leading to a rooty tumor:
A rooty tumor suggests a phenotype where root development is favoured. This occurs when the ratio of auxin to cytokinin is high. If mutating gene X leads to this phenotype, it means that the normal function of gene X is to counteract this high auxin/low cytokinin state or to promote the opposite. If gene X normally produces cytokinin, its mutation would lead to reduced cytokinin levels. With reduced cytokinin, the auxin level (presumably maintained by gene Y) would be relatively higher, resulting in a high auxin/low cytokinin ratio, which promotes root formation. Therefore, gene X likely encodes cytokinins.
Mutation of Gene Y leading to shoots in the tumor:
The appearance of shoots in the tumor suggests a phenotype where shoot development is favoured. This occurs when the ratio of auxin to cytokinin is low. If mutating gene Y leads to this phenotype, it means that the normal function of gene Y is to counteract this low auxin/high cytokinin state or to promote the opposite. If gene Y normally produces auxin, its mutation would lead to reduced auxin levels. With reduced auxin, the cytokinin level (presumably maintained by gene X) would be relatively higher, resulting in a low auxin/high cytokinin ratio, which promotes shoot formation. Therefore, gene Y likely encodes auxins.
Connecting Genes to Hormones
Based on the analysis of the mutation effects and the known roles of plant hormones in differentiation:
- Mutation of Gene X (results in rooty tumor) implies Gene X normally produces cytokinin.
- Mutation of Gene Y (results in shoots in tumor) implies Gene Y normally produces auxin.
Thus, Gene 'X' encodes cytokinins and Gene 'Y' encodes auxins.
Let's summarize this relationship:
| Gene | Mutation Effect | Implied Function | Resulting Hormone Ratio (Mutation) | Phenotype Explanation |
|---|---|---|---|---|
| X | Rooty tumor | Encodes Cytokinin | High Auxin / Low Cytokinin | Reduced Cytokinin from mutated X gene shifts ratio towards root formation. |
| Y | Shoots in tumor | Encodes Auxin | Low Auxin / High Cytokinin | Reduced Auxin from mutated Y gene shifts ratio towards shoot formation. |
This conclusion aligns with the functions of hormone synthesis genes found in the T-DNA of Agrobacterium tumefaciens, where genes like ipt (isopentenyl transferase) are involved in cytokinin synthesis and genes like iaaM and iaaH are involved in auxin synthesis.
Important Questions from Transgenic animals and plants
An experiment was performed to introduce a transgenic trait in a crop plant by Agrobacterium-mediated transformation using a transgene construct in which the transgene was expressed using the CaMV 35S promoter. It was observed that expression levels of the transgenic protein were very low in all transgenic plants while transgene mRNA levels were high and variable among different plants. Further, different transgenic lines contained different numbers of the T-DNA insert. The following statements were made to explain the above observation:
A. Variations in the number of T-DNA inserts in different transgenic plants is due to more number of host cells getting infected with the T-DNA
B. Low expression levels of the transgenic protein in all transgenic plants could be due to codon usage variations between the host plant and the heterologous source of the transgene
C. The coding sequence of the transgene contained sequences that destabilized the transgene mRNA
D. Variation in copy number of T-DNA in different transgenic plants is due to variation in the promoter used to express the transgene.
Which one of the following options represents all correct
statements?Following statements were given regarding factors influencing variation in expression levels of transgene in transgenic plants:
A. Difference in restriction enzyme sites within the T-DNA.
B. Difference in copy number of the transgene.
C. Variations in site of integration of the T-DNA within the plant genome.
D. Presence of multiple promoters within the T-DNA region.
Which one of the following options represents a combination of statements that would NOT lead to variations in transgene expression levels in transgenic plants generated using the same T-DNA/binary vector?
Which one of the following statements related to genetic transformation of plants is correct?
The following statements are made regarding developing a transgenic mouse:
A. The transgenic mouse thus born will be a homozygous transgenic animal and can be maintained by crossing with another transgenic animal.
B. The fertilized transgenic eggs are allowed to develop in vitro.
C. The desired gene is preferably microinjected in male pronucleus after sperm entry in oocyte.
D. For best efficiency, the desired gene is always microinjected in the male gametes and then they are allowed to fertilize the female gametes.
E. Blastocyst stage embryos are transferred to the uterus of hormonally prepared mother.
F. The fertilized eggs are collected from specific strain of mouse.
G. The female mouse of specific strain is superovulated, oocytes are collected and allowed to fertilize in vitro.
Choose the combination of statements arranged in the correct sequence for developing transgenic mouse.
Which one of the following genomes is most appropriate to determine hybrids in plants and animals?
