Disassembly of the fruit cell wall by the ripening-associated polygalacturonase and expansin influences tomato cracking. Issue 1 (1st February 2019)

• Record Type: Journal Article
• Authors: Jiang, Fangling; Lopez, Alfonso; Jeon, Shinjae; de Freitas, Sergio Tonetto; Yu, Qinghui; Wu, Zhen; Labavitch, John M; Tian, Shengke; Powell, Ann L T; Mitcham, Elizabeth
• Is Part Of: Horticulture research. Volume 6:Issue 1(2019)
• Publication Date: 2019-02-01
• Subjects: Transgenic organisms -- Translation; Horticulture -- Research -- Periodicals; 635.072
• DOI: 10.1038/s41438-018-0105-3
• Languages: English
• ISSNs: 2052-7276

Abstract

Abstract: Fruit cracking is an important problem in horticultural crop production. Polygalacturonase (SlPG) and expansin (SlEXP1) proteins cooperatively disassemble the polysaccharide network of tomato fruit cell walls during ripening and thereby, enable softening. A Golden 2-like (GLK2) transcription factor, SlGLK2 regulates unripe fruit chloroplast development and results in elevated soluble solids and carotenoids in ripe fruit. To determine whether SlPG, SlEXP1, or SlGLK2 influence the rate of tomato fruit cracking, the incidence of fruit epidermal cracking was compared between wild-type, Ailsa Craig (WT) and fruit with suppressed SlPG and SlEXP1 expression ( pg/exp ) or expressing a truncated nonfunctional Slglk2 ( glk2 ). Treating plants with exogenous ABA increases xylemic flow into fruit. Our results showed that ABA treatment of tomato plants greatly increased cracking of fruit from WT and glk2 mutant, but not from pg/exp genotypes. The pg/exp fruit were firmer, had higher total soluble solids, denser cell walls and thicker cuticles than fruit of the other genotypes. Fruit from the ABA treated pg/exp fruit had cell walls with less water-soluble and more ionically and covalently-bound pectins than fruit from the other lines, demonstrating that ripening-related disassembly of the fruit cell wall, but not elimination of SlGLK2, influences cracking. Cracking incidence was significantly correlated with cell wall and wax thickness, and the content of cell wall protopectin and cellulose, but not with Ca 2+ content. Crop genetics: Keeping tomato skins together: Researchers in the USA reveal a link between cell wall composition and splitting skin in ripe tomatoes, known as cracking. To unravel the mechanism behind cracking, a team led by Elizabeth Mitcham of the University of California, Davis, compared wild-type tomato plants, mutant plants with increased soluble solids, and mutant plants with altered cell wall structure. They treated the three lines with the hormone ABA to induce cracking and measured several traits in the fruit. ABA treatment did not affect cracking incidence in the cell wall mutant but increased its frequency in the other two lines. Cell wall composition and thickness were the traits with the strongest correlation with cracking rate. Altogether, these findings show that cell wall structure is a major determinant of cracking and point the way towards reducing skin splitting in tomatoes.