Disassembly of the fruit cell wall by the ripening-associated polygalacturonase and expansin influences tomato cracking

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 Ca2+ content.

LncRNA regulates tomato fruit cracking by coordinating gene expression via a hormone-redox-cell wall network

“…These genes play important roles in cell wall loosing and expansion. As disassembly of the fruit cell wall can influence fruit cracking [30], These plant cell-wall loosing genes may also play a key regulatory role in tomato fruit cracking. At the same time, we used Tomato Gene Expression Atlas (http://tea.solgenomics.net/expression_viewer/input) to verify the gene expression, and found that most differentially expressed genes in this experiment were expressed in tomato pericarp in red ripe stage.…”

“…Then, 9 DEGs were randomly selected from the DEGs to verify the RNA-seq results. Gene-specific primers were designed using Premier 5.0 [98] and actin as a reference gene [30]. The relative levels of gene expression were calculated using the 2 -ΔΔCT method [99] .…”

“…Simultaneous suppression of SlPG and SlEXP1 expression in ripening fruits reduces cell wall disassembly and thereby reduces the fruit cracking rate by approximately 12% [30]. It is not a single gene but many genes working together that regulate fruit cracking [30][31][32][33]. It remains unclear whether there are other genes related to fruit cracking and which one is the major gene.…”

LncRNA regulates tomato fruit cracking by coordinating gene expression via a hormone-redox-cell wall network

“…Then, 9 DEGs were randomly selected from the DEGs to verify the RNA-seq results. Gene-specific primers were designed using Premier 5.0 [99] and actin as a reference gene [30]. The relative levels of gene expression were calculated using the 2 -ΔΔCT method [100] .…”

Decrease in cell size and cell wall components under ectopic expression of the CaRLK1 gene

“…Such hormones as auxins, gibberellins, ethylene, and cytokinins direct the coordinated growth and proliferation of plant cells. Expansins [8] and polygalacturonase (PG) [9] are known to be responsible for loosening the structure of the wall.…”