ROS-mediated Lignin Biosynthesis is Associated with Cell Wall Expansion in Asian Pear (Pyrus pyrifolia Nakai) During Fruit Development and Ripening

Abstract

Fruit growth and development is regulated by cell expansion, which is a culmination of balanced cell stiffening and loosening. Reactive oxygen species (ROS) are crucial factors regulating cell expansion. In the present study, we investigated how cell wall expansion is regulated by ROS homeostasis in two Asian pear (Pyrus pyrifolia Nakai) cultivars with different maturity periods. ROS production, lignin contents, peroxidase activity, and gene expression levels were measured during pear fruit development and ripening. An increase in fruit fresh weight was observed 72 and 87 days after full bloom (DAFB) in early-maturing cultivar 'Wonhwang' and late-maturing cultivar 'Niitaka', respectively; the former exhibited higher weights than the latter until 132 DAFB. In both cultivars, ROS (O 2•and H 2 O 2 ) content gradually decreased up to 132 DAFB; higher levels were detected in 'Niitaka' than in 'Wonhwang', which was consistent with the superoxide dismutase (SOD) activity. H 2 O 2 -induced lignin content decreased after maintaining a high level up to 87 DAFB in 'Niitaka', whereas it continued to decrease during fruit development and ripening after 57 DAFB in 'Wonhwang'. In 'Niitaka', activities of lignin biosynthesis-related enzymes, guaiacol peroxidase (GPOX) and coniferyl alcohol peroxidase (CPOX), rapidly decreased from 102 to 132 DAFB, but remained higher than those in 'Wonhwang'; this result was consistent with the expression patterns of peroxidase genes (PpPOX1 and PpPOX4). The expression level of the cell wall loosening-related gene, expansin 1 (PpEXP1), was elevated only in the middle stage of fruit development and ripening, while the expression level of xyloglucan endotransglucosylases 1 (PpXET1) rapidly increased after 57 and 87 DAFB in 'Wonhwang' and 'Niitaka', respectively. These results indicate that ROS-mediated lignin synthesis through peroxidase is associated with cell wall expansion in Pyrus pyrifolia.

Different Activities of Pectin-degrading Enzymes Affecting the Growth of Asian Pears

“…The rate, duration, and plane orientation of cell division as well as the direction and degree of cell expansion are key parameters that profoundly affect the final fruit size (van der Knaap and Østergaard, 2018). The final fruit size is also influenced by cell wall component assembly and disassembly processes involving pectin, hemicellulose, and cellulose (Goulao and Oliveira, 2008;Brahem et al, 2017;Lee et al, 2022). Lahaye et al (2021) explained that fruit firmness declines with cell wall polysaccharide remodeling, which is disassembled by enzyme consortia and various non-enzymatic mechanisms during fruit growth and development.…”