Abstract
Fruit size is largely defined by the number and size of cells in the fruit. Endoreduplication – a specialized cell cycle – is highly associated with cell expansion during tomato fruit growth. However, how endoreduplication coupled with cell size is regulated remains poorly understood. In this study, we identified a zinc finger gene SlPZF1 (SolanumlycopersicumPERICARP-ASSOCIATEDZINCFINGER PROTEIN 1) that was highly expressed in the pericarp of developing fruits. Plants with altered SlPZF1 expression produced smaller fruits due to the reduction in cell size associated with weakened endoreduplication. Overexpressing SlPZF1 delayed cell division phase by enhancing early expression of several key cell cycle regulators including SlCYCD3;1 and two plant specific mitotic cyclin-dependent protein kinase (SlCDKB1 and SlCDKB2) in the pericarp tissue. Furthermore, we identified 14 putative SlPZF1 interacting proteins (PZFIs) via yeast two hybrid screening. Several PZFIs, including Pre-mRNA-splicing factor (SlSMP1/PZFI4), PAPA-1-like conserved region family protein (PZFI6), Fanconi anemia complex components (PZFI3 and PZFI10) and bHLH transcription factor LONESOME HIGHWAY (SlLHW/PZFI14), are putatively involved in cell cycle regulation. Our results demonstrate that fruit growth in tomato requires balanced expression of the novel cell size regulator SlPZF1.
Highlights
Tomato (Solanum lycopersicum) is one of the most important vegetable crops cultivated world-wide, which (2021) 1:6 domestication and breeding improvement (Tanksley 2004)
Core SlPZF1 encodes a member of C2H2 zinc finger protein family, preferentially expressed in the pericarp during tomato fruit development
SlPZF1 was mainly expressed in pericarp during early fruit growth We previously identified a set of putative transcription factors that were preferentially expressed in developing fruits (Xiao et al 2009)
Summary
Tomato (Solanum lycopersicum) is one of the most important vegetable crops cultivated world-wide, which (2021) 1:6 domestication and breeding improvement (Tanksley 2004). Two cloned fruit size QTLs in tomato impact fruit mass through the regulation of cell division. Gain-of-function mutation in fw11.3 allele (fw11.3-D) increases fruit weight cell size through its positive regulation of pericarp cell size (Mu et al 2017). The enlargement of pericarp cells is associated with higher DNA ploidy in these cells, indicating that fw11.3 may be involved in cell cycle regulation. Despite the progress in the identification of genetic loci controlling fruit size, the regulatory mechanism underlying cell division and expansion during tomato fruit development is still not well understood. Given there is a strong positive correlation between cell size and ploidy level, it has been hypothesized that endoreduplication is likely one of the major driving forces to increase cell size in tomato fruit. DNA ploidy level is not always associated with cell size; high DNA ploidy due to enhanced endoreduplication may cause either no or subtle changes in cell size (De Veylder et al 2001; Leiva-Neto et al 2004)
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