Reduced phototropism in pks mutants may be due to altered auxin‐regulated gene expression or reduced lateral auxin transport

Abstract

SUMMARYPhototropism allows plants to orient their photosynthetic organs towards the light. In Arabidopsis, phototropins 1 and 2 sense directional blue light such that phot1 triggers phototropism in response to low fluence rates, while both phot1 and phot2 mediate this response under higher light conditions. Phototropism results from asymmetric growth in the hypocotyl elongation zone that depends on an auxin gradient across the embryonic stem. How phototropin activation leads to this growth response is still poorly understood. Members of the phytochrome kinase substrate (PKS) family may act early in this pathway, because PKS1, PKS2 and PKS4 are needed for a normal phototropic response and they associate with phot1 in vivo. Here we show that PKS proteins are needed both for phot1-and phot2-mediated phototropism. The phototropic response is conditioned by the developmental asymmetry of dicotyledonous seedlings, such that there is a faster growth reorientation when cotyledons face away from the light compared with seedlings whose cotyledons face the light. The molecular basis for this developmental effect on phototropism is unknown; here we show that PKS proteins play a role at the interface between development and phototropism. Moreover, we present evidence for a role of PKS genes in hypocotyl gravi-reorientation that is independent of photoreceptors. pks mutants have normal levels of auxin and normal polar auxin transport, however they show altered expression patterns of auxin marker genes. This situation suggests that PKS proteins are involved in auxin signaling and/or lateral auxin redistribution.

Plant Flavoprotein Photoreceptors

“…In addition to ABCB19, members of the Phytochrome Kinase Substrate (PKS) family have also been shown to play a role in phototropism. PKS4 is rapidly phosphorylated by phot1 in response to blue light and is proposed to impact phototropism positively or negatively depending on its phosphorylation status (Demarsy et al 2012, Kami et al 2014). The biochemical function of PKS proteins is presently unknown, but they probably impact auxin signaling or transport (Kami et al 2014).…”

Shining Light on the Function of NPH3/RPT2-Like Proteins in Phototropin Signaling

“…While PKS proteins are required for phytochrome signaling (Lariguet et al, 2003;Schepens et al, 2008), some of the phenotypes associated with pks mutants resemble those of nph3, rpt2, and phot-deficient mutants. For instance, the pks1 pks2 pks4 triple mutant exhibits reduced phototropic curvature (Lariguet et al, 2006;Kami et al, 2014). PKS1 and PKS2 also act in concert with NPH3 to establish leaf positioning and leaf expansion (de Carbonnel et al, 2010).…”

“…Resolving the biochemical functions of these proteins and how they integrate with NPH3 and RPT2 will be important to fully understand how phots initiate signaling from the plasma membrane. Like NPH3, PKS proteins are suggested to modulate auxin transport or signaling (de Carbonnel et al, 2010;Kami et al, 2014). Yet, their mechanism of action in this regard remains to be elucidated.…”

ArabidopsisDNA topoisomerase i alpha is required for adaptive response to light and flower development

“…Several studies have demonstrated that PKSs serve as a molecular link between phytochrome and phototropin-mediated responses through interaction with phytochromes and PHOT1 (Lariguet et al, 2006; Demarsy et al, 2012; Kami et al, 2014). PKSs may contribute to the phototropic response regulation through modulation of local auxin signaling or transport (Kami et al, 2014). Hence, light can effectively coordinate the activity of major auxin transporters and therefore auxin distribution to control phototropic responses in different organs (Žádníková et al, 2015).…”