Role of Actin Cytoskeleton in Brassinosteroid Signaling and in Its Integration with the Auxin Response in Plants

Abstract

In plants, developmental programs and tropisms are modulated by the phytohormone auxin. Auxin reconfigures the actin cytoskeleton, which controls polar localization of auxin transporters such as PIN2 and thus determines cell-type-specific responses. In conjunction with a second growth-promoting phytohormone, brassinosteroid (BR), auxin synergistically enhances growth and gene transcription. We show that BR alters actin configuration and PIN2 localization in a manner similar to that of auxin. We describe a BR constitutive-response mutant that bears an allele of the ACTIN2 gene and shows altered actin configuration, PIN2 delocalization, and a broad array of phenotypes that recapitulate BR-treated plants. Moreover, we show that actin filament reconfiguration is sufficient to activate BR signaling, which leads to an enhanced auxin response. Our results demonstrate that the actin cytoskeleton functions as an integration node for the BR signaling pathway and auxin responsiveness.

9-Lipoxygenase-derived oxylipins activate brassinosteroid signaling to promote cell wall-based defense and limit pathogen infection

“…Characterization of noxy mutants showed that the 9-LOX pathway participates in signaling cell wall damage (Vellosillo et al, 2013). These 9-LOX pathway characteristics parallel the functions reported for BRs, whose signaling is triggered as part of a compensatory mechanism to maintain cell wall integrity; application of 24-epibrassinolide (BL; an active BR) to Arabidopsis seedlings induces root waving that resembles the oxylipin phenotype (Lanza et al, 2012;Wolf et al, 2012;Wolf and Höfte, 2014). These observations suggested that the 9-LOX and BR pathways share signaling components.…”

Brassinosteroid signalling

“…Fourth, BZR2 and ARF5 bind to the same BR/auxin-response promoter [SMALL AUXIN UPREGULATED15 (SAUR15)] (Walcher and Nemhauser, 2012). Fifth, BR and auxin responses are integrated through the actin cytoskeleton, which is not only regulated by both BR and auxin but also feedback regulates auxin transport and BR signalling (Lanza et al, 2012). The contributions of these mechanisms to the physiology of BR-auxin interaction remain to be evaluated further.…”

Effect of n-butanol and cold pretreatment on the cytoskeleton and the ultrastructure of maize microspores when cultured in vitro

“…This complex system has diverse roles in the life of a cell: takes part in the formation of cell shape, sets up and maintains cell polarity, transports organelles, and coordinates cell division (Kost and Chua 2002). New functions of the cytoskeleton were found recently, such as phytohormone signalization (Lanza et al 2012) and programmed cell death (Smertenko and FranklinTong 2011). Nevertheless, there is a lack of information on the relation of the plant cytoskeleton and abiotic stresses, although the effects of salt and osmotic stresses (Wang et al 2011) and heat stress (Malerba et al 2010) are studied in some types of vegetative cells.…”