SlSLAH1 Defines SlSTOP1-Activated Malate Exudation Pathway for Aluminium Tolerance in Tomato

Area of Science:

• Plant Biology
• Molecular Genetics
• Soil Science

Background:

• Aluminum (Al) toxicity in acidic soils inhibits plant growth and productivity.
• Organic acid exudation, particularly malate, is a key Al-tolerance mechanism in plants.
• The specific transporters and regulatory networks governing malate exudation in tomato (Solanum lycopersicum) are not well understood.

Purpose of the Study:

• To identify and characterize the malate transporters and regulatory factors involved in Al tolerance in tomato.
• To elucidate the molecular mechanisms underlying Al-induced malate exudation in tomato roots.
• To provide insights for developing Al-tolerant tomato germplasm.

Main Methods:

• Identification of SlSLAH1 as a plasma membrane-localized malate transporter.
• Analysis of SlSTOP1 and SlSZP1 complex formation and binding to the SlSLAH1 promoter under Al stress.
• Investigation of SlSLAH2 expression, interaction with SlSLAH1, and its role in malate exudation.
• Genetic analysis using knockout mutants and overexpression lines of Slslah1 and Slslah2.

Main Results:

• SlSLAH1 was identified as a crucial malate transporter essential for Al tolerance.
• The SlSTOP1-SlSZP1 complex directly activated SlSLAH1 expression, enhancing root malate exudation under Al stress.
• SlSLAH2 formed a heteromeric complex with SlSLAH1, synergistically increasing malate exudation.
• Mutants lacking SlSLAH1 or SlSLAH2 showed reduced malate exudation and increased Al sensitivity.
• Overexpression of SlSLAH1 conferred enhanced Al tolerance in tomato.

Conclusions:

• A novel regulatory module involving the SlSTOP1-SlSZP1 complex and the SlSLAH1-SlSLAH2 heteromeric complex orchestrates malate exudation for Al tolerance in tomato.
• This study provides mechanistic insights into Al detoxification pathways in plants.
• The findings offer a foundation for breeding Al-tolerant tomato varieties.