Question:
Evolutionarily linked Genome Reduction is observed in __________.
(A) Xylella
(B) Phytoplasma
(C) Phytophthora
(D) Magnaporthe
Choose the correct answer from the options given below :
Evolutionarily linked Genome Reduction is observed in __________.
(A) Xylella
(B) Phytoplasma
(C) Phytophthora
(D) Magnaporthe
Choose the correct answer from the options given below :
(A) Xylella
(B) Phytoplasma
(C) Phytophthora
(D) Magnaporthe
Choose the correct answer from the options given below :
Show Hint
Phytoplasmas have lost so many essential metabolic genes during reductive evolution that they cannot be cultured on cell-free artificial media in the laboratory.
They can only be maintained within their living plant hosts or insect vectors.
They can only be maintained within their living plant hosts or insect vectors.
Updated On: Jul 23, 2026
- (A) and (B) only.
- (A), (B) and (D) only.
- (A), (B), (C) and (D).
- (B), (C) and (D) only.
Show Solution
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept:
Genome reduction is an evolutionary process where organisms lose genes that are redundant or unnecessary for survival in their specific ecological niche.
This is commonly observed in obligate intracellular parasites, vascular-limiting endosymbionts, or highly specialized pathogens that rely on their host's metabolic machinery to survive.
Step 2: Detailed Explanation:
Let us analyze each of the listed organisms to evaluate genome reduction:
(A) Xylella:
Xylella fastidiosa is a xylem-limiting bacterium transmitted by insect vectors.
Living in a nutrient-restricted, highly specialized niche within xylem vessels and insect foreguts, it has undergone significant genome reduction.
It has lost many metabolic pathways, relying on the host plant and vector to supply essential amino acids and nutrients.
Thus, (A) exhibits evolutionary genome reduction.
(B) Phytoplasma:
Phytoplasmas are specialized, wall-less, phloem-limiting bacteria transmitted by insect vectors.
They are obligate parasites that have undergone extreme reductive evolution.
They possess some of the smallest genomes among self-replicating prokaryotes (typically $530 - 1350\text{ kb}$), having lost genes for cell wall synthesis, the tricarboxylic acid (TCA) cycle, and fatty acid biosynthesis.
They rely entirely on the nutrient-rich phloem of the host plant to meet their metabolic needs.
Thus, (B) exhibits evolutionary genome reduction.
(C) Phytophthora & (D) Magnaporthe:
These are large, complex eukaryotic pathogens with relatively large genomes (typically $100 - 240\text{ Mb}$ for *Phytophthora* and $40\text{ Mb}$ for *Magnaporthe*) containing extensive gene families, including duplicated effector genes and secretomes.
They have not undergone significant reductive evolution.
Thus, (A) and (B) are the primary examples of evolutionary genome reduction.
Step 3: Final Answer:
Evolutionarily linked genome reduction is observed in Xylella and Phytoplasma ((A) and (B) only).
This corresponds to Option (1).
Genome reduction is an evolutionary process where organisms lose genes that are redundant or unnecessary for survival in their specific ecological niche.
This is commonly observed in obligate intracellular parasites, vascular-limiting endosymbionts, or highly specialized pathogens that rely on their host's metabolic machinery to survive.
Step 2: Detailed Explanation:
Let us analyze each of the listed organisms to evaluate genome reduction:
(A) Xylella:
Xylella fastidiosa is a xylem-limiting bacterium transmitted by insect vectors.
Living in a nutrient-restricted, highly specialized niche within xylem vessels and insect foreguts, it has undergone significant genome reduction.
It has lost many metabolic pathways, relying on the host plant and vector to supply essential amino acids and nutrients.
Thus, (A) exhibits evolutionary genome reduction.
(B) Phytoplasma:
Phytoplasmas are specialized, wall-less, phloem-limiting bacteria transmitted by insect vectors.
They are obligate parasites that have undergone extreme reductive evolution.
They possess some of the smallest genomes among self-replicating prokaryotes (typically $530 - 1350\text{ kb}$), having lost genes for cell wall synthesis, the tricarboxylic acid (TCA) cycle, and fatty acid biosynthesis.
They rely entirely on the nutrient-rich phloem of the host plant to meet their metabolic needs.
Thus, (B) exhibits evolutionary genome reduction.
(C) Phytophthora & (D) Magnaporthe:
These are large, complex eukaryotic pathogens with relatively large genomes (typically $100 - 240\text{ Mb}$ for *Phytophthora* and $40\text{ Mb}$ for *Magnaporthe*) containing extensive gene families, including duplicated effector genes and secretomes.
They have not undergone significant reductive evolution.
Thus, (A) and (B) are the primary examples of evolutionary genome reduction.
Step 3: Final Answer:
Evolutionarily linked genome reduction is observed in Xylella and Phytoplasma ((A) and (B) only).
This corresponds to Option (1).
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