Diverse Functions of IAA-Leucine Resistant PpILR1 Provide a Genic Basis for Auxin-Ethylene Crosstalk During Peach Fruit Ripening.

Xiaobei Wang,Yan Wang,Wenfang Zeng,Nicolaas Jacobus Nieuwenhuizen,Zhiqiang Wang,Li Deng,Junren Meng,Jia-Long Yao,Hui Liu

doi:10.3389/fpls.2021.655758

Abstract

Auxin and ethylene play critical roles in the ripening of peach (Prunus persica) fruit; however, the interaction between these two phytohormones is complex and not fully understood. Here, we isolated a peach ILR gene, PpILR1, which encodes an indole-3-acetic acid (IAA)-amino hydrolase. Functional analyses revealed that PpILR1 acts as a transcriptional activator of 1-amino cyclopropane-1-carboxylic acid synthase (PpACS1), and hydrolyzes auxin substrates to release free auxin. When Cys137 was changed to Ser137, PpILR1 failed to show hydrolase activity but continued to function as a transcriptional activator of PpACS1 in tobacco and peach transient expression assays. Furthermore, transgenic tomato plants overexpressing PpILR1 exhibited ethylene- and strigolactone-related phenotypes, including premature pedicel abscission, leaf and petiole epinasty, and advanced fruit ripening, which are consistent with increased expression of genes involved in ethylene biosynthesis and fruit ripening, as well as suppression of branching and growth of internodes (related to strigolactone biosynthesis). Collectively, these results provide novel insights into the role of IAA-amino acid hydrolases in plants, and position the PpILR1 protein at the junction of auxin and ethylene pathways during peach fruit ripening. These results could have substantial implications on peach fruit cultivation and storage in the future.

Highlights

Ethylene plays a critical role in controlling the ripening climacteric fruits (Tucker et al, 2017)
The results showed that PpILR1 bound to the PpACS1-P1 fragment (Figure 1B)
In the Y1H assay, only PpILR1-1–120aa interacted with PpACS1-P1 (Figure 1E), which suggested that PpILR1-1–120aa was the domain that directly interacted with PpACS1-P1

Summary

Introduction

Ethylene plays a critical role in controlling the ripening climacteric fruits (Tucker et al, 2017). ACS is unstable and exhibits very low levels in tissues that do not produce large amounts of ethylene; under conditions that promote ethylene biosynthesis, the activity of ACS is highly elevated. Auxin has long been considered to counteract fruit ripening; a recent transcriptomic approach highlighted a previously underestimated role of auxin during regulation of fruit ripening in peach (Prunus persica) (Trainotti et al, 2007). Low levels of IAA lead to suppression of PpACS1 expression at the late-ripening stage of stony hard peach, whereas high concentrations of IAA are required for ethylene biosynthesis, which results in rapid fruit softening (Tatsuki et al, 2013; Pan et al, 2015). Since the auxin-ethylene relationship is very intricate, some of the phenotypic effects are yet to be assigned to either hormone

Methods

Results

Conclusion