Aluminum (Al) stress is a global problem that inhibits root growth and crop production in acidic soils. The inhibitive effect is greatly attributed to the reduction of cell wall elasticity. The present study aimed to investigate the function of a polygalacturonase gene MsPG4 in regulating cell wall extensibility and alfalfa resistance to Al stress.
The transgenic alfalfa plants of overexpression (MsPG4-OE) and knockdown (MsPG4-RNAi) of MsPG4 were treated with or without 100 µM AlCl3. The methods of field emission scanning electron microscope, transmission electron microscope and atomic force microscopy were used in physiological and histological analysis.
The relative root elongation was higher in MsPG4-OE lines and lower in MsPG4-RNAi lines than wild type (WT) plants under Al stress. Al contents in root tips and cell wall decreased in MsPG4-OE lines but increased in MsPG4-RNAi lines, which positively related to their pectin contents. The contents of water soluble pectin (WSP) and chelator soluble pectin (CSP) decreased in MsPG4-OE lines and increased in MsPG4-RNAi lines in the absence or presence of Al compared to WT plants. Consequently, the dimensions of the two pectin’s molecules reduced, the porosity and extensibility of cell wall increased in MsPG4-OE lines comparted to WT plants under Al stress.
MsPG4 effectively increases the cell wall extensibility and Al resistance of alfalfa via hydrolysis of pectins in the cell wall.