High-lysine/high-methionine corn — identify the relevant mutants Which choice correctly names the maize mutants known to increase lysine and/or methionine content in corn endosperm proteins?

Introduction / Context:
Native maize zein proteins are low in essential amino acids like lysine and methionine. Classical genetic mutants such as opaque-2 and floury-2 alter endosperm protein composition, increasing nutritionally valuable amino acids and inspiring quality protein maize (QPM) breeding efforts.

Given Data / Assumptions:

• Opaque-2 (o2) reduces zein synthesis and elevates non-zein proteins richer in lysine.
• Floury-2 (fl2) also modifies storage protein assembly and content.
• Other listed mutants affect starch or lignin and are not primarily high-lysine/methionine sources.

Concept / Approach:

By decreasing the proportion of zeins (deficient in lysine), o2 and fl2 mutants shift the proteome toward albumins and glutelins with higher lysine. Some QPM lines combine o2 with modifiers to restore kernel hardness while maintaining improved amino acid balance.

Step-by-Step Solution:

Verification / Alternative check:

Nutrition analyses of o2/fl2 kernels show elevated essential amino acids relative to normal maize, supporting the answer.

Why Other Options Are Wrong:

Sugary-1 and shrunken-2 primarily affect carbohydrate metabolism; brown midrib influences lignin, not seed amino acid profile.

Common Pitfalls:

Assuming any endosperm phenotype equates to protein quality improvement; only specific mutants alter amino acid profiles beneficially.

Final Answer:

Opaque-2 and Floury-2 mutants