Bifunctional transcription factors SlERF.H5 and H7 activate cell wall and repress gibberellin biosynthesis genes in tomato via a conserved motif.

The plant cell wall is a dynamic structure that plays an essential role in development, but the mechanism regulating cell wall formation remains poorly understood. We demonstrate that two transcription factors, SlERF.H5 and SlERF.H7, control cell wall formation and tomato fruit firmness in an additive manner. Knockout of SlERF.H5, SlERF.H7, or both genes decreased cell wall thickness, firmness, and cellulose contents in fruits during early development, especially in double-knockout lines. Overexpressing either gene resulted in thicker cell walls and greater fruit firmness with elevated cellulose levels in fruits but severely dwarf plants with lower gibberellin contents. We further identified that SlERF.H5 and SlERF.H7 activate the cellulose biosynthesis gene SlCESA3 but repress the gibberellin biosynthesis gene GA20ox1. Moreover, we identified a conserved LPL motif in these ERFs responsible for their activities as transcriptional activators and repressors, providing insight into how bifunctional transcription factors modulate distinct developmental processes.

Ethylene-MPK8-ERF.C1-PR module confers resistance against Botrytis cinerea in tomato fruit without compromising ripening.

The plant hormone ethylene plays a critical role in fruit defense against Botrytis cinerea attack, but the underlying mechanisms remain poorly understood. Here, we showed that ethylene response factor SlERF.C1 acts as a key regulator to trigger the ethylene-mediated defense against B. cinerea in tomato fruits without compromising ripening. Knockout of SlERF.C1 increased fruit susceptibility to B. cinerea with no effect on ripening process, while overexpression enhanced resistance. RNA-Seq, transactivation assays, EMSA and ChIP-qPCR results indicated that SlERF.C1 activated the transcription of PR genes by binding to their promoters. Moreover, SlERF.C1 interacted with the mitogen-activated protein kinase SlMPK8 which allowed SlMPK8 to phosphorylate SlERF.C1 at the Ser174 residue and increases its transcriptional activity. Knocking out of SlMPK8 increased fruit susceptibility to B. cinerea, whereas overexpression enhanced resistance without affecting ripening. Furthermore, genetic crosses between SlMPK8-KO and SlERF.C1-OE lines reduced the resistance to B. cinerea attack in SlERF.C1-OE fruits. In addition, B. cinerea infection induced ethylene production which in turn triggered SlMPK8 transcription and enhanced the phosphorylation of SlERF.C1. Overall, our findings reveal the regulatory mechanism of the 'Ethylene-MPK8-ERF.C1-PR' module in resistance against B. cinerea and provide new insight into the manipulation of gray mold disease in fruits.

ß-1,3-GLUCANASE10 regulates tomato development and disease resistance by modulating callose deposition.

ß-1,3-Glucanases are considered key regulators responsible for the degradation of callose in plants, yet little is known about the role and mode of action of their encoding genes in tomato (Solanum lycopersicum). In the present study, we identified the ß-1,3-glucanase encoding gene ß-1,3-GLUCANASE10 (SlBG10) and revealed its regulation in tomato pollen and fruit development, seed production, and disease resistance by modulating callose deposition. Compared with wild-type (WT) or SlBG10 overexpressing (SlBG10-OE) lines, knockout of SlBG10 caused pollen arrest and failure to set fruit with reduced male rather than female fecundity. Further analyses showed that SlBG10-knockout promoted callose deposition in anther at the tetrad-to-microspore stages, resulting in pollen abortion and male sterility. Moreover, loss-of-function SlBG10 delayed degradation of endosperm cell wall calloses during cellularization and impeded early seed development. We also uncovered that Botrytis cinerea infection induces SlBG10 expression in WT tomato, and the knockout lines showed increased callose accumulation in fruit pericarps, reduced susceptibility to B. cinerea, and enhanced antioxidant capacity to maintain tomato fruit quality. However, the expression of genes encoding cell wall hydrolases decreased in SlBG10-knockout tomatoes and thus led to an increase in pericarp epidermal thickness, enhancement in fruit firmness, reduction of fruit water loss, and extension of tomato shelf life. These findings not only expand our understanding of the involvement of ß-1,3-glucanases as callose regulators in multiple developmental processes and pathogen resistance but also provide additional insight into the manipulation of multiagronomic traits for targeted tomato breeding.