Keren-Keiserman, A. | Search bioRxiv

bioRxiv2022

Solanum lycopersicum CLASS-II KNOX genes regulate fruit anatomy via gibberellin-dependent and independent pathways.

The pericarp is the predominant tissue determining the structural characteristics of most fruits. However, the molecular and genetic mechanisms controlling pericarp development remain only partially understood. Previous studies have identified that CLASS-II KNOX genes regulate fruit size, shape, and maturation in Arabidopsis thaliana and Solanum lycopersicum. Here we characterized the roles of the Solanum lycopersicum CLASS-II KNOX (TKN-II) genes in pericarp development via a detailed histological, anatomical, and karyotype analysis of the TKN-II knockdown (35S:amiR-TKN-II) fruits. We identify that 35S:amiR-TKN-II pericarps contain more cells around their equatorial perimeter and fewer cell layers than the control. In addition, the cell sizes but not the ploidy levels of these pericarps were dramatically reduced. Further, we demonstrate that fruit shape and pericarp layer number phenotypes of the 35S:amiR-TKN-II fruits can be overridden by the procera mutant, known to induce a constitutive response to the plant hormone gibberellin. However, neither the procera mutation nor exogenous gibberellin application can fully rescue the reduced pericarp width and cell size phenotype of 35S:amiR-TKN-II pericarps. Our findings establish that TKN-II genes regulate tomato fruit anatomy, acting via gibberellin to control fruit shape but utilizing a gibberellin-independent pathway to control the size of pericarp cells. HighlightTomato CLASS-II KNOX genes regulate fruit and pericarp anatomy via GA-dependent and independent pathways.

plant biology↗

bioRxiv2021

CLASS-II KNOX genes coordinate spatial and temporal patterns of the tomato ripening

Ripening is a complex developmental change of a mature organ, the fruit. In plants like a tomato, it involves softening, pigmentation, and biosynthesis of metabolites beneficial for the human diet. Examination of the transcriptional changes towards ripening suggests that redundant uncharacterized factors may be involved in the coordination of the ripening switch. Previous studies have demonstrated that Arabidopsis CLASS-II KNOX genes play a significant role in controlling the maturation of siliques and their transition to senescence. Here we examined the combined role of all four tomato CLASS-II KNOX genes in the maturation and ripening of fleshy fruits using an artificial microRNA targeting them simultaneously. As expected, the knockdown plants (35S::amiR-TKN-CL-II) exhibited leaves with increased complexity, reminiscent of the leaf phenotype of plants overexpressing CLASS-I KNOX, which antagonize CLASS-II KNOX gene functions. The fruits of 35S::amiR-TKN-CL-II plants were notably smaller than the control. While their internal gel/placenta tissue softened and accumulated the typical pigmentation, the pericarp color break took place ten days later than control, and eventually, it turned yellow instead of red. Additionally, the pericarp of 35S::amiR-TKN-CL-II fruits remained significantly firmer than control even after three weeks of shelf storage. Strikingly, the 35S::amiR-TKN-CL-II fruits showed early ethylene release and respiration peak, but these were correlated only with liquefaction and pigmentation of the internal tissues. Our findings suggest that CLASS-II KNOX genes are required to coordinate the spatial and temporal patterns of tomato fruit ripening. One sentence summaryTomato CLASS-II KNOX genes play antagonistic roles in the regulation of ripening at the internal fruit domains and pericarp.

developmental biology↗