Q&A: Auxin: the plant molecule that influences almost anything

Abstract

Auxin is an essential molecule that controls almost every aspect of plant development. Although the core signaling components that control auxin response are well characterized, the precise mechanisms enabling specific responses are not yet fully understood. Considering the significance of auxin in plant growth and its potential applications, deciphering further aspects of its biology is an important and exciting challenge.

Fig. 1

Auxin homeostasis is essential for proper development. Drawings of a wild-type seedling and an adult plant (center of the figure in green) and some characterized mutants for auxin homeostasis (in boxes). Mutants with affected auxin biosynthesis are in light brown boxes. sur1 is an overproducer [5] while wei8 tar2 [6] is depleted of auxin. Signaling mutants are shown in light blue boxes and are mutated in the auxin transcription factor 5 (arf5/monopteros) [25], auxin transcriptional inhibitor iaa14 (or solitary root) [26], or the auxin co-receptors (tir1, afb2, afb3) [27]. Mutants for influx (aux1) [28] and efflux auxin transporters (pin1) [7] are shown in the light red boxes

Fig. 2

The nuclear auxin pathway (NAP) is the machinery that controls auxin gene expression. Without auxin (a), the transcriptional functions of the auxin response factors (ARF, in blue) are inhibited by the Aux/IAA proteins (in red) through heterodimerization. When auxin enters the nucleus (b), it allows binding between Aux/IAAs and the SCF (TIR/AFBs) complex (in green). These co-receptors will subsequently be degraded, allowing the ARF to modulate auxin-related gene expression