Role of PIN-mediated auxin efflux in apical hook development ofArabidopsis thaliana

Abstract

SUMMARYThe apical hook of dark-grown Arabidopsis seedlings is a simple structure that develops soon after germination to protect the meristem tissues during emergence through the soil and that opens upon exposure to light. Differential growth at the apical hook proceeds in three sequential steps that are regulated by multiple hormones, principally auxin and ethylene. We show that the progress of the apical hook through these developmental phases depends on the dynamic, asymmetric distribution of auxin, which is regulated by auxin efflux carriers of the PIN family. Several PIN proteins exhibited specific, partially overlapping spatial and temporal expression patterns, and their subcellular localization suggested auxin fluxes during hook development. Genetic manipulation of individual PIN activities interfered with different stages of hook development, implying that specific combinations of PIN genes are required for progress of the apical hook through the developmental phases. Furthermore, ethylene might modulate apical hook development by prolonging the formation phase and strongly suppressing the maintenance phase. This ethylene effect is in part mediated by regulation of PIN-dependent auxin efflux and auxin signaling.

Ethylene inhibits lateral root development, increases IAA transport and expression of PIN3 and PIN7 auxin efflux carriers

“…This suggests increased auxin synthesis and reduced auxin transport contribute to the elevation of auxin signaling that mediates the reduction in growth after ACC treatment (Ruzicka et al, 2007;Stepanova et al, 2007;Swarup et al, 2007). Ethylene also inhibits other auxin-dependent process including hypocotyl and root gravity response (Buer et al, 2006;Li, 2008;, root waving (Buer et al, 2003) and hypocotyl hook opening Zadnikova et al, 2010). By contrast, root hair development is stimulated by both auxin and ethylene (Rahman et al, 2002).…”

Phototropin 1 and dim-blue light modulate the red light de-etiolation response

“…These mutants were chosen because of their cognate gene expression patterns in the hook/hypocotyl area. [19][20][21] Meanwhile the auxin response factor mutant arf7/nph4 was also included for the test based on its role in phototropism response. 22,23 Generally, the transporter mutants maintained a normal or near normal B light negation effect to R light.…”

Shedding light on auxin movement: Light-regulation of polar auxin transport in the photocontrol of plant development

“…The formation of the apical hook is caused by asymmetrical growth of the cells on the two opposing sides of the upper part of the hypocotyl. 23,24 The differential growth response coincides with the establishment of an auxin signaling maximum on the concave side of the apical hook, dependent on transport of auxin synthesized in cotyledons. [23][24][25] The expression and the polar localization of several PINs is dynamically regulated during the establishment of the apical hook, but only PIN3 has been demonstrated to play a key role in the early stages of apical hook formation, whereas PIN1, PIN4 and PIN7 play redundant roles in the maintenance of the hook folding.…”

“…23,24 The differential growth response coincides with the establishment of an auxin signaling maximum on the concave side of the apical hook, dependent on transport of auxin synthesized in cotyledons. [23][24][25] The expression and the polar localization of several PINs is dynamically regulated during the establishment of the apical hook, but only PIN3 has been demonstrated to play a key role in the early stages of apical hook formation, whereas PIN1, PIN4 and PIN7 play redundant roles in the maintenance of the hook folding. 23,25 Relevantly, auxin influx carrier proteins AUX1 and LAX3 and ABCB/PGP efflux facilitators ABCB19 and ABCB1 have been The growth conditions and microscopy used for this experiment were previously described.…”

“…23,24,31,42 On the other hand, in undifferentiated tissues such as meristems and leaf primordia, light-mediated control of PIN protein abundance through the regulation of vacuolar degradation is likely to specifically and reversibly regulate auxin fluxes and as a result growth, without affecting meristem patterning. 28,34,35,37,38 Another interesting aspect that is surfacing from these studies is that the environmental control of plant growth relies on common auxin transport-dependent regulatory mechanisms.…”