Betaine deficiency in maize : complementation tests and metabolic basis

Area of Science:

• Plant biochemistry
• Genetics
• Maize (Zea mays L.) research

Background:

• Maize is typically a betaine-accumulating species.
• Some maize genotypes exhibit a near-complete deficiency in betaine.
• A single recessive gene was previously suggested to cause this betaine deficiency.

Purpose of the Study:

• To investigate if betaine deficiency in various maize germplasm is controlled by a common genetic locus.
• To identify the specific biochemical pathway affected in betaine-deficient maize.
• To understand the genetic basis of betaine synthesis in maize.

Main Methods:

• Complementation tests were performed on 13 betaine-deficient maize genotypes.
• A segregating maize population (P77) was used to create betaine-positive and betaine-deficient lines.
• Enzymatic assays were conducted using supplied betaine aldehyde and choline on leaf tissues.

Main Results:

• Complementation tests confirmed that all 13 deficient maize genotypes share a common genetic locus for betaine deficiency.
• Betaine-positive and betaine-deficient lines could convert betaine aldehyde to betaine.
• Only betaine-positive lines could oxidize choline to betaine, indicating the lesion is at the choline to betaine aldehyde conversion step.
• Betaine-deficient plants showed no detectable endogenous betaine aldehyde pool.

Conclusions:

• Betaine deficiency in diverse maize germplasm is controlled by a single, common genetic locus.
• The biochemical lesion in betaine-deficient maize is located in the enzyme catalyzing the oxidation of choline to betaine aldehyde.
• This genetic defect disrupts the initial step of betaine synthesis in maize.