Overexpression of PpSnRK1α in Tomato Promotes Fruit Ripening by Enhancing RIPENING INHIBITOR Regulation Pathway.

Wen Yu,Guifang Wang,Futian Peng,Yuansong Xiao,Jingjing Luo

doi:10.3389/fpls.2018.01856

Abstract

As a conserved kinase complex, sucrose non-fermenting-1-related protein kinase 1 (SnRK1) is a major regulator of plant growth and development. In our previous study, overexpression of MhSnRK1 in tomato (Solanum lycopersicum L.) modified fruit maturation: the transgenic fruit ripened earlier than the wild type (WT). However, the mechanism by which fruit maturation is regulated by SnRK1 is not clear; therefore, the test materials used were the transgenic tomato lines (OE-1, OE-3, and OE-4) overexpressing the coding gene of peach [Prunus persica (L.) Batsch] SNF1-related kinase α subunit (PpSnRK1α). The activity of SnRK1 kinase in transgenic tomato lines OE-1, OE-3, and OE-4 was higher than that in the WT at different periods of fruit development; in the pink coloring period the SnRK1 kinase activity increased the most, with 23.5, 28.8, and 21.4% increases, respectively. The content of starch and soluble sugars in red ripe transgenic fruit significantly increased, while the soluble protein and titratable acid content decreased significantly. We also found that the tomatoes overexpressing PpSnRK1α matured approximately 10 days earlier than the WT. Moreover, the yeast-two-hybrid assay showed that PpSnRK1α interacted with the MADS-box transcription factor (TF) SIRIN, which acts as an essential regulator of tomato fruit ripening. The BiFC technology further validated the location of the PpSnRK1α interaction sites within the nucleus. The quantitative real-time PCR analysis showed that RIN expression was up-regulated by PpSnRK1α overexpression; the expression of RIN-targeted TF genes NOR and FUL1 increased during different stages of fruit development. The expression of key genes, ACS2, ACS4, and E8, in ethylene synthesis also changed accordingly, and the ethylene emitted by the red ripe fruit increased by 36.1–43.9% compared with the WT. These results suggest that PpSnRK1α interacts with SIRIN, increasing the expression of RIN, thereby regulating the expression of downstream ripening-related genes, finally promoting fruit ripening.

Highlights

Sucrose non-fermenting 1 kinase (SNF1)-related kinase (SnRK1) in plants belongs to a conserved family that includes SNF1 in yeast and AMP-activated protein kinase in animals (Crozet et al, 2014)
Does SnRK1 interact with the transcription factor (TF) ripening inhibitor (RIN), regulating fruit ripening? Using PpSnRK1α overexpressing tomato lines (OE-1, OE-3, and OE-4) and wild type (WT) tomato as test material, we examined the relationship between SnRK1 and RIN and we speculate that SnRK1 regulates fruit maturation by affecting the RIN regulation pathway
In the early stage of fruit development, the diameter of the transgenic tomato fruit was significantly larger than that of the WT, but there was no significant difference in fruit size between the two since the green mature stage (Figure 1C)

Summary

Introduction

Sucrose non-fermenting 1 kinase (SNF1)-related kinase (SnRK1) in plants belongs to a conserved family that includes SNF1 in yeast and AMP-activated protein kinase in animals (Crozet et al, 2014). Previous studies have shown that SnRK1 may play a key role in the overall regulation of the intracellular sugar signaling pathway and metabolism, and regulates plant carbohydrate metabolism (Ramon et al, 2013; Emanuelle et al, 2016). Many studies have shown that plant SnRK1 is involved in many metabolic pathways including carbohydrate metabolism, stress, organogenesis, and senescence pathways (Purcell et al, 1998; Laurie et al, 2003; Jossier et al, 2009; Broeckx et al, 2016). This study was the first to show that SnRK1 affects fruit ripening (Wang et al, 2012)

Methods

Results

Conclusion