D6PK AGCVIII Kinases Are Required for Auxin Transport and Phototropic Hypocotyl Bending in Arabidopsis    

Abstract

Phototropic hypocotyl bending in response to blue light excitation is an important adaptive process that helps plants to optimize their exposure to light. In Arabidopsis thaliana, phototropic hypocotyl bending is initiated by the blue light receptors and protein kinases phototropin1 (phot1) and phot2. Phototropic responses also require auxin transport and were shown to be partially compromised in mutants of the PIN-FORMED (PIN) auxin efflux facilitators. We previously described the D6 PROTEIN KINASE (D6PK) subfamily of AGCVIII kinases, which we proposed to directly regulate PIN-mediated auxin transport. Here, we show that phototropic hypocotyl bending is strongly dependent on the activity of D6PKs and the PIN proteins PIN3, PIN4, and PIN7. While early blue light and phot-dependent signaling events are not affected by the loss of D6PKs, we detect a gradual loss of PIN3 phosphorylation in d6pk mutants of increasing complexity that is most severe in the d6pk d6pkl1 d6pkl2 d6pkl3 quadruple mutant. This is accompanied by a reduction of basipetal auxin transport in the hypocotyls of d6pk as well as in pin mutants. Based on our data, we propose that D6PK-dependent PIN regulation promotes auxin transport and that auxin transport in the hypocotyl is a prerequisite for phot1-dependent hypocotyl bending.

Phospholipid composition and a polybasic motif determine D6 PROTEIN KINASE polar association with the plasma membrane and tropic responses

“…d6pk d6pkl1 (d6pk01) or d6pk d6pkl1 d6pkl2 (d6pk012) mutants are impaired in auxin transport-dependent growth responses, including negative gravitropism and phototropism of the hypocotyl. Expression of YFP:D6PK from a D6PK promoter fragment is sufficient to suppress these phenotypes in d6pk012 (Willige et al, 2013). Likewise, YFP:D6PK-3KA, when expressed from the D6PK promoter, suppressed the tropism defects of the d6pk01 mutant efficiently (Fig.…”

“…The AGCVIII serine/threonine kinase D6 PROTEIN KINASE (D6PK) but also the proposed PIN polarity regulator PINOID (PID) activate PIN-mediated auxin transport through PIN phosphorylation when tested in Xenopus laevis oocytes (Friml et al, 2004;Zourelidou et al, 2014). Arabidopsis mutants of D6PK and the orthologous D6PK-LIKE genes D6PKL1-D6PKL3 are compromised in directional auxin transport and PIN-dependent growth (Willige et al, 2013;Zourelidou et al, 2009). Conversely, pharmacological interference with D6PK abundance at the plasma membrane impairs auxin transport-dependent tropic responses .…”

Neighbor Detection Induces Organ-Specific Transcriptomes, Revealing Patterns Underlying Hypocotyl-Specific Growth

“…We used the following Arabidopsis thaliana genotypes (cv Columbia-0): pin3 pin4 pin7, d6pk01, D6PK-OX (Willige et al, 2013), sav3-2 (Tao et al, 2008), pif7-1 (Li et al, 2012), DII-VENUS (Brunoud et al, 2012), pif4 pif5 pif7 (de Wit et al, 2015), amiD2/5/7/8/9 (Spartz et al, 2014), amiSAUR19/23/24 (Spartz et al, 2012), and iYUC3 (FRO6:XVE:YUC3; Chen et al, 2014). To generate the yuc2 yuc5 yuc8 yuc9 quadruple mutant, T-DNA and transposon insertion lines were obtained from the ABRC, the Cold Spring Harbor Laboratory, or GABI-Kat.…”

Dynamic PIN-FORMED auxin efflux carrier phosphorylation at the plasma membrane controls auxin efflux-dependent growth

“…as with decreases in directional auxin transport in stems and hypocotyls (13,16,17). Thus, PIN1 phosphorylation is essential for auxin transport in planta and may allow predicting PIN1 activity in situ.…”

“…Genetic studies indicate that D6PK acts in a functionally redundant manner with at least three other sequence-related D6PK-LIKE genes (12,16,17). Based on genetic and cell biological studies, functional redundancy was also proposed between PID, WAG1, and WAG2, and possibly with PID2, which are all members of a distinct subclade within the Arabidopsis AGCVIII protein kinase family (30,31).…”