Mutation of the Polygalacturonase Gene AcoPG3 Deferred Softening of Pineapple Fruit

A large number of pineapple (<i>Ananas comosus</i>) fruits are discarded in China every year due to softening. However, the underlying molecular mechanism is still unknown. <i>AcoPG3</i> (GenBank accession number: XM020243935), a pineapple gene of polygalacturonase, was found to be the major gene responsible for the softening of pineapple fruit. Fruit of <i>AcoPG3</i>-overexpressing tomato (<i>Solanum lycopersicum</i> var. Jingfan 101) begins to soften 9 days earlier than that transformed with a net vector. Fruit of <i>AcoPG3</i>-overexpressing pineapple (APG3-2) begins to soften 6 days earlier than that transformed with a net vector. Fruit of MPG3-1, a pineapple line in which <i>AcoPG3</i> is mutated, begins to soften 31 days later than that transformed with a net vector. The sequence of polygalacturonase activities in fruit from the highest to the lowest was APG3-2, wild type, MPG3-1. The same sequences were also found in the liquid content of apoplast and the electrolyte leakage of pineapple pulp. The order of methyl-esterified pectin content in the pulp cell wall, from the highest to the lowest, was MPG3-1, wild type, and APG3-2. The same order was also observed for the contents of non-methyl-esterified homogalacturonan and rhamnogalacturonan-I in the pulp cell wall. The <i>AcoPG3</i> mutation resulted in a decrease in polygalacturonase activity in pineapple fruit, decreasing the degradation of methyl-esterified pectin, non-methyl-esterified homogalacturonan, galactan and rhamnogalacturonan-I in the pulp cell wall. Fruit softening can be deferred, and the shelf life can be extended by mutating the <i>AcoPG3</i> gene.