Expansin SlExp1 and endoglucanase SlCel2 synergistically promote fruit softening and cell wall disassembly in tomato

Abstract

Fruit softening, an irreversible process that occurs during fruit ripening, can lead to losses and waste during postharvest transportation and storage. Cell wall disassembly is the main factor leading to loss of fruit firmness, and several ripening-associated cell wall genes have been targeted for genetic modification, particularly pectin modifiers. However, individual knockdown of most cell wall–related genes has had minimal influence on cell wall integrity and fruit firmness, with the notable exception of pectate lyase. Compared to pectin disassembly, studies of the cell wall matrix, the xyloglucan–cellulose framework, and underlying mechanisms during fruit softening are limited. Here, a tomato (Solanum lycopersicum) fruit ripening–associated α-expansin (SlExpansin1/SlExp1) and an endoglucanase (SlCellulase2/SlCel2), which function in the cell wall matrix, were knocked out individually and together using clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated nuclease 9-mediated genome editing. Simultaneous knockout of SlExp1 and SlCel2 enhanced fruit firmness, reduced depolymerization of homogalacturonan-type pectin and xyloglucan, and increased cell adhesion. In contrast, single knockouts of either SlExp1 or SlCel2 did not substantially change fruit firmness, while simultaneous overexpression of SlExp1 and SlCel2 promoted early fruit softening. Collectively, our results demonstrate that SlExp1 and SlCel2 synergistically regulate cell wall disassembly and fruit softening in tomato.

Recent Advances in Tomato Gene Editing

“…Conversely, simultaneous overexpression of these genes promoted early fruit softening. These results support the conclusion that these two genes have a synergistic effect on fruit softening [ 141 ]. Furthermore, the bHLH transcription factor BRI1-EMS-SUPPRESSOR1 (BES1) encoded by Solyc04g079980 has been identified as an upstream regulator of fruit softening through the activation of cell-wall degradation during ripening [ 142 ].…”

“…However, only mutations in the PL gene Solyc03g111690 , resulted in firmer fruits [ 140 ]. Simultaneous knockout of two genes, one encoding a fruit ripening-associated α-expansin ( Solyc06g051800 ) and the other an endoglucanase ( Solyc09g010210 ), using CRISPR/Cas9 improved fruit firmness [ 141 ]. Conversely, simultaneous overexpression of these genes promoted early fruit softening.…”

Exploring the PpEXPs Family in Peach: Insights into Their Role in Fruit Texture Development through Identification and Transcriptional Analysis

“…The expression of the four candidate EXPs dramatically increased when firmness decreased in strawberries [30]. In tomatoes, SlEXP1 promoted fruit softening cooperating with SlCel2 [18]. It is worth noting that ethylene responsive elements and abscisic acid responsive elements were detected in the promoter region of PpEXPA7, PpEXPA13 and PpEXPA15; therefore, we propose that PpEXPs might be involved in regulating fruit textures in peaches.…”

“…There is increasing evidence that softening is a complex process that involves multiple genes. PG, PME, PL, β-galactosidase arabinofuranosidase and expansin have been proven to be involved in the softening of tomatoes [13][14][15][16][17][18].…”

Application of L-Cysteine Hydrochloride Delays the Ripening of Harvested Tomato Fruit

“…Various crucial hydrolases, such as polygalacturonase (PG), pectin methylesterase (PME), pectate lyase (PL), β-galactosidase (TBG), endotransglycosylase (XTH), and endo-glucanase (CEL), are responsible for cellular wall disassembly during fruit ripening [ 45 , 46 ]. In addition, Expansin (EXP) also plays a role in the regulation of fruit softening [ 47 ]. In this study, we observed that treatment with LCH led to the upregulation of cell wall degradation-related genes such as PG2a , PL , PL8 , TBG4 , and EXP1 , contributing to the delayed ripening of tomato fruit.…”