Maize Carbohydrate partitioning defective1 impacts carbohydrate distribution, callose accumulation, and phloem...

Area of Science:

• Plant Biology
• Molecular Genetics
• Biochemistry

Background:

• Plants synthesize carbohydrates in leaves and transport them to other tissues for growth.
• Genes controlling whole-plant carbohydrate partitioning are largely unknown.
• Sucrose transport is crucial for plant development.

Purpose of the Study:

• Identify genes controlling carbon export from plant leaves.
• Investigate the function of the Carbohydrate partitioning defective1 (Cpd1) gene in maize.
• Understand the mechanisms of whole-plant carbohydrate partitioning.

Main Methods:

• Screening of mutagenized maize plants for altered carbohydrate transport.
• Phenotypic analysis including chlorosis and sugar accumulation.
• Phloem transport experiments.
• Callose deposition analysis.
• Benzoxazinoid quantification and double mutant analysis.

Main Results:

• A semi-dominant mutant, Cpd1, was identified with reduced carbohydrate transport.
• Cpd1 mutants exhibit hyperaccumulation of starch and soluble sugars in leaves due to inhibited sucrose export.
• Ectopic callose deposits were observed in the phloem of Cpd1 mutants, likely impairing transport.
• Cpd1 mutants also overaccumulate benzoxazinoids and show increased aphid tolerance, independently of callose accumulation.
• Callose accumulation and carbon hyperaccumulation are independent of benzoxazinoid production.

Conclusions:

• The Cpd1 gene plays a critical role in regulating sucrose export from maize leaves.
• Callose deposition in the phloem is a key factor in inhibiting long-distance carbohydrate transport in Cpd1 mutants.
• The cpd1 gene likely functions early in phloem development, influencing whole-plant carbohydrate partitioning.
• Cpd1 has pleiotropic effects, impacting both carbohydrate transport and defense compound production.