Ethylene in vegetative development: a tale with a riddle

Contents Summary 895 I. Introduction 895 II. A snapshot view on the ethylene biosynthesis and signaling pathway in Arabidopsis 896 III. Autocontrol of ethylene biosynthesis 897 IV. Mechanistic control of ethylene signal components 898 V. The auxinethylene circle 901 VI. Tissue- and cell-type-specific regulation of ethylene 903 VII. Cellular basis of ethylene effects on growth 904 Acknowledgements 906 References 906 Summary The vegetative development of plants is strongly dependent on the action of phytohormones. For over a century, the effects of ethylene on plants have been studied, illustrating the profound impact of this gaseous hormone on plant growth, development and stress responses. Ethylene signaling is under tight self-control at various levels. Feedback regulation occurs on both biosynthesis and signaling. For its role in developmental processes, ethylene has a close and reciprocal relation with auxin, another major determinant of plant architecture. Here, we discuss, in view of novel findings mainly in the reference plant Arabidopsis, how ethylene is distributed and perceived throughout the plant at the organ, tissue and cellular levels, and reflect on how plants benefit from the complex interaction of ethylene and auxin, determining their shape. Furthermore, we elaborate on the implications of recent discoveries on the control of ethylene signaling.