Cytokinin treatments affect the apical-basal patterning of the Arabidopsis gynoecium and resemble the effects of polar auxin transport inhibition.

Victor M Zãºã±Iga-Mayo,Stefan De Folter,Nayelli Marsch-Martinez,J Irepan Reyes-Olalde

doi:10.3389/fpls.2014.00191

Abstract

The apical-basal axis of the Arabidopsis gynoecium is established early during development and is divided into four elements from the bottom to the top: the gynophore, the ovary, the style, and the stigma. Currently, it is proposed that the hormone auxin plays a critical role in the correct apical-basal patterning through a concentration gradient from the apical to the basal part of the gynoecium, as chemical inhibition of polar auxin transport through 1-N-naphtylphtalamic acid (NPA) application, severely affects the apical-basal patterning of the gynoecium. In this work, we show that the apical-basal patterning of gynoecia is also sensitive to exogenous cytokinin (benzyl amino purine, BAP) application in a similar way as to NPA. BAP and NPA treatments were performed in different mutant backgrounds where either cytokinin perception or auxin transport and perception were affected. We observed that cytokinin and auxin signaling mutants are hypersensitive to NPA treatment, and auxin transport and signaling mutants are hypersensitive to BAP treatment. BAP effects in apical-basal gynoecium patterning are very similar to the effects of NPA, therefore, it is possible that BAP affects auxin transport in the gynoecium. Indeed, not only the cytokinin-response TCS::GFP marker, but also the auxin efflux carrier PIN1 (PIN1::PIN1:GFP) were both affected in BAP-induced valveless gynoecia, suggesting that the BAP treatment producing the morphological changes has an impact on both in the response pattern to cytokinin and on auxin transport. In summary, we show that cytokinin affects proper apical-basal gynoecium patterning in Arabidopsis in a similar way to the inhibition of polar auxin transport, and that auxin and cytokinin mutants and markers suggest a relation between both hormones in this process.

Highlights

IntroductionDifferent axes can be distinguished during the development of the Arabidopsis thaliana gynoecium and one of them is the apicalbasal axis
The gynoecium is the female reproductive organ of the flower
Because the role of naphtylphtalamic acid (NPA) is to block polar auxin transport and the phenotypes caused by both benzyl amino purine (BAP) and NPA treatments are similar, the results suggest that exogenously applied cytokinin might affect polar auxin transport and thereby cause the observed patterning phenotypes

Summary

Introduction

Different axes can be distinguished during the development of the Arabidopsis thaliana gynoecium and one of them is the apicalbasal axis. This axis can be divided into four domains: the stigma at the apical part, consisting of a single layer of elongated cells called papillae, followed by a solid cylinder below, called the style, there is the ovary which is the most complex part of the gynoecium and contains the ovules, and in the basal part the gynophore, which is a short stalk-like structure connecting the gynoecium with the rest of the plant (Balanza et al, 2006; Roeder and Yanofsky, 2006; Alvarez-Buylla et al, 2010). Alterations in the apical-basal patterning of the gynoecium are distinguished by an increase in the style and gynophore domain sizes at the expense of the ovary, which in severe cases even completely disappears

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