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

Authors: SU, GUANQUING - Zheijiang University; LIN, YIFAN - Zheijiang University; WANG, CHUNFENG - Zheijiang University; LU, JIAO - Zheijiang University; LIU, ZIMENG - Zheijiang University; HE, ZHIREN - Zheijiang University; XIU, SHU - Zheijiang University; CHEN, WENBO - Zheijiang University; WU, RONGRONG - Zheijiang University; LI, BAIJUN - Zheijiang University; ZHU, CHANGQING - Zheijiang University; ROSE, JOCELYN - Cornell University; GRIERSON, DONALD - University Of Nottingham; Giovannoni, James; SHI, YANNA - Zheijiang University; CHEN, KUNSONG - Zheijiang University

Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2023
Publication Date: 3/3/2024
Citation: Su, G., Lin, Y., Wang, C., Lu, J., Liu, Z., He, Z., Xiu, S., Chen, W., Wu, R., Li, B., Zhu, C., Rose, J., Grierson, D., Giovannoni, J.J., Shi, Y., Chen, K. 2024. Expansin SlExp1 and endoclucanase SlCel2 synergistically promote fruit softening and cell wall disassembly in tomato. The Plant Cell. 36 (3) 709-726. https://doi.org/10.1093/plcell/koad291.
DOI: https://doi.org/10.1093/plcell/koad291

Interpretive Summary: Fruit softening is an irreversible process that occurs during ripening and reduces transportability and shelf life. Disassembly of the cell wall is key in the loss of fruit firmness, and several ripening-associated cell wall–modifying genes have been targeted for genetic modification, particularly pectin modifiers. However, except for pectate lyase, single knockouts of most ripening-associated cell wall genes do not affect cell wall integrity and fruit firmness. HEre we demonstrate that two genes of tomato, SlExp1 and SlCel2, synergistically regulate cell wall disassembly and tomato fruit softening. Moreover, modulating SlExp1 and SlCel2 did not alter plant growth and development, fruit taste, or quality-related traits, suggesting a viable approach to enhance fruit texture without sacrificing quality.

Technical 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 a-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.