Functional FTSH4 complexes in Arabidopsis mitochondria: a megacomplex with SLP1 and SLP1-free smaller complexes

Area of Science:

• Mitochondrial biology
• Plant science
• Proteostasis

Background:

• FTSH4 protease is key to Arabidopsis mitochondrial protein quality control.
• It possesses both proteolytic and chaperone activities, forming inner mitochondrial membrane complexes.

Purpose of the Study:

• Investigate the assembly of FTSH4 into distinct complexes.
• Determine the functional roles of these FTSH4 assemblies in Arabidopsis mitochondria.

Main Methods:

• Analysis of FTSH4 assembly in wild-type and slp1-1 mutant Arabidopsis.
• Assessing mitochondrial protein levels (TIM17-2, NAD9) and protein aggregates (HSP23.6).
• Evaluating the mitochondrial unfolded protein response and plant morphology.

Main Results:

• FTSH4 assembles into a megacomplex with SLP1 and SLP1-free assemblies.
• slp1-1 mutants lack the FTSH4-SLP1 megacomplex but show increased SLP1-free FTSH4, retaining proteolytic activity.
• slp1-1 mitochondria exhibit reduced heat-induced protein aggregation and lack the unfolded protein response.

Conclusions:

• SLP1-free FTSH4 assemblies are sufficient for general mitochondrial proteostasis and heat protection.
• The FTSH4-SLP1 megacomplex is specialized for meristem-specific functions.
• Distinct FTSH4 complexes mediate different cellular roles in Arabidopsis mitochondria.