SlPIN1 regulates auxin efflux to affect flower abscission process

Zihang Shi,Ruishu Cao,Tianlai Li,Yun Jiang,Mingfang Qi,Tao Xu,Xin Liu,Xinqi Han

doi:10.1038/s41598-017-15072-7

Zihang Shi, Ruishu Cao + Show 6 more

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https://doi.org/10.1038/s41598-017-15072-7

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Abstract

Solanum lycopersicum PIN-FORMED1 (SlPIN1), a major auxin efflux facilitator, contributes to the establishment of auxin maxima during organ initiation and development in tomato. However, the functions of SlPIN1 during organ abscission remain unclear. In our study, SlPIN1 expression decreased immediately after flower removal and increased following IAA treatment, indicating a high sensitivity to auxin depletion. 1-MCP (an ethylene inhibitor) delayed abscission and down-regulated SlPIN1, indicating that ethylene may positively regulate SlPIN1 and that low expression levels of SlPIN1 may delay abscission. The SlPIN1 protein levels were not consistent with the expression pattern, implying that in addition to transcription, protein degradation also affects SlPIN1 levels during abscission. The phosphorylation of SlPIN1 at Ser418, which significantly declined during abscission, was found to play roles in SlPIN1 localization and auxin transport. We also identified the interaction proteins of SlPIN1, which were involved in phosphorylation and ubiquitylation. Therefore, complex mechanisms mediate SlPIN1 auxin transport capability during abscission. The silencing of SlPIN1 expression accelerated abscission by increasing auxin accumulation in the ovary and decreasing the auxin content in the abscission zone (AZ), indicating that SlPIN1 plays a major role in mediating auxin source-sink transport and the establishment and maintenance of auxin maxima in the AZ.

Highlights

Polar auxin transport (PAT) controls developmental events, such as root formation[1,2], leaf morphogenesis[3], vascular formation and patterning[4,5,6], fruit development[7,8] and seed dispersal[9], by creating auxin maxima and minima
To characterize the expression pattern of Solanum lycopersicum PIN-FORMED1 (SlPIN1) in the tomato pedicel during abscission, flower pedicel explants were sampled 0–24 h after flower removal, and SlPIN1 expression in the distal part, the abscission zone (AZ) and the proximal part were analysed by quantitative real-time PCR (RT-PCR)
After 4 h, SlPIN1 was up-regulated in the AZ and proximal part, while its expression remained low in the distal part for 24 h (Fig. 1b,c,d, Control)

Summary

Introduction

Polar auxin transport (PAT) controls developmental events, such as root formation[1,2], leaf morphogenesis[3], vascular formation and patterning[4,5,6], fruit development[7,8] and seed dispersal[9], by creating auxin maxima and minima. While the roles played by ethylene in the abscission process have been reported[11,13,16,17], the influence of ethylene on pedicel auxin transport and PIN expression remains unknown. Overexpression of PID or phosphomimetic substitutions at the PID phosphorylated sites of PIN1 result in a basal-to-apical shift of PIN1 localization in Arabidopsis[39,45], while dephosphorylation induced by PP2A has an antagonistic function[40]. Other kinases, such as the D6PKs, affect the auxin transport activity of PIN rather than its localization[41]. Knowledge regarding PIN ubiquitylation in other PINs or other physiological processes is limited

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