Fruit Architecture in Polyamine-Rich Tomato Germplasm Is Determined via a Medley of Cell Cycle, Cell Expansion, and Fruit Shape Genes.

Raheel Anwar,Avtar K Handa,Shazia Fatima,Autar K Mattoo

doi:10.3390/plants8100387

Abstract

Shape and size are important features of fruits. Studies using tomatoes expressing yeast Spermidine Synthase under either a constitutive or a fruit-ripening promoter showed obovoid fruit phenotype compared to spherical fruit in controls, suggesting that polyamines (PAs) have a role in fruit shape. The obovoid fruit pericarp exhibited decreased cell layers and pericarp thickness compared to wild-type fruit. Transgenic floral buds and ovaries accumulated higher levels of free PAs, with the bound form of PAs being predominant. Transcripts of the fruit shape genes, SUN1 and OVATE, and those of CDKB2, CYCB2, KRP1 and WEE1 genes increased significantly in the transgenic ovaries 2 and 5 days after pollination (DAP). The levels of cell expansion genes CCS52A/B increased at 10 and 20 DAP in the transgenic fruits and exhibited negative correlation with free or bound forms of PAs. In addition, the cell layers and pericarp thickness of the transgenic fruits were inversely associated with free or bound PAs in 10 and 20 DAP transgenic ovaries. Collectively, these results provide evidence for a linkage between PA homeostasis and expression patterns of fruit shape, cell division, and cell expansion genes during early fruit development, and suggest role(s) of PAs in tomato fruit architecture.

Highlights

Domestication of tomato has led to different phenotypes, including diversity in fruit shape, color, and size [1]
The cellular levels of bound Put, Spd, and Spm correlate with CDKA1, CDKB2, CYCB2, KRP1, and WEE1 transcripts, but not CCS52A, CCS52B, CYCA2, and CYCD3 genes in transgene-associated change in fruit shape
The patterns of gene expression during early fruit development indicate that the upregulated CDKB2 may in turn activate CYCB2 expression during ovary development at 2 days after pollination (DAP)

Summary

Introduction

Domestication of tomato has led to different phenotypes, including diversity in fruit shape, color, and size [1]. A mutation in the FW2.2 promoter inhibits cell division during flower development and causes a larger fruit phenotype [15]. Another gene SUN1 encodes a protein harboring an IQ67 domain and affects cell number along the entire proximal-distal axis, resulting in fruit elongation [16,17,18]. OVATE family proteins (OFPs) and TONNEAU1 Recruiting Motif proteins affect fruit shape by regulating cell division patterns during ovary development [19,20].

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