Mitochondrial complex I assembles via a distal-pump module (P_D)-early and P_D-late pathway in maize

Area of Science:

• Mitochondrial Biology
• Protein Complex Assembly
• Plant Biochemistry

Background:

• Mitochondrial complex I (CI) is L-shaped with matrix (N, Q modules) and membrane (P_P, P_D modules) arms.
• The CI assembly pathway in plants remains largely uncharacterized due to a lack of suitable mutants.

Purpose of the Study:

• To elucidate the assembly pathway of mitochondrial complex I in maize.
• To identify the roles of specific assembly factors in CI biogenesis.

Main Methods:

• Utilized maize RNA processing mutants deficient in individual CI components.
• Employed complexome profiling to detect assembly intermediates.
• Isolated and analyzed mutants of CI assembly factors ZmGLDH and CRK1.

Main Results:

• Complexome profiling confirmed independent assembly pathways for each CI module.
• Defects in Q module assembly led to membrane arm accumulation; P_D module defects caused CI* accumulation.
• ZmGLDH and CRK1 are essential for the P_D-late assembly pathway, preventing CI* accumulation and facilitating CI formation.

Conclusions:

• Two distinct CI assembly pathways, P_D-early and P_D-late, were identified in maize.
• The P_D-early pathway involves initial assembly of the membrane arm (P_P + P_D) followed by matrix arm integration.
• The P_D-late pathway, dependent on ZmGLDH and CRK1, involves initial assembly of P_P with the matrix arm to form CI*, subsequently integrating P_D.