Gibberellin Regulates PIN-FORMED Abundance and Is Required for Auxin Transport–Dependent Growth and Development inArabidopsis thaliana   

Abstract

Plants integrate different regulatory signals to control their growth and development. Although a number of physiological observations suggest that there is crosstalk between the phytohormone gibberellin (GA) and auxin, as well as with auxin transport, the molecular basis for this hormonal crosstalk remains largely unexplained. Here, we show that auxin transport is reduced in the inflorescences of Arabidopsis thaliana mutants deficient in GA biosynthesis and signaling. We further show that this reduced auxin transport correlates with a reduction in the abundance of PIN-FORMED (PIN) auxin efflux facilitators in GA-deficient plants and that PIN protein levels recover to wild-type levels following GA treatment. We also demonstrate that the regulation of PIN protein levels cannot be explained by a transcriptional regulation of the PIN genes but that GA deficiency promotes, at least in the case of PIN2, the targeting of PIN proteins for vacuolar degradation. In genetic studies, we reveal that the reduced auxin transport of GA mutants correlates with an impairment in two PINdependent growth processes, namely, cotyledon differentiation and root gravitropic responses. Our study thus presents evidence for a role of GA in these growth responses and for a GA-dependent modulation of PIN turnover that may be causative for these differential growth responses.

Lysine 63 -linked ubiquitylation of PIN2 auxin carrier protein governs hormonally controlled adaptation of Arabidopsis root growth

“…This process involves constitutive protein cycling and transcytosis that affect auxin flow by altering distribution of PMlocalized and intracellular PIN protein pools (13,14), whereas PIN ubiquitylation could act as a rate-limiting determinant for spatiotemporal control of PIN degradation. A number of recent reports connected light and growth regulator signaling to vacuolar sorting of PIN proteins (25,33,34), substantiating a scenario in which multiple pathways impinge on PIN protein degradation to orchestrate auxin distribution in a multifaceted developmental context. Variations in PIN polyubiquitylation might function as a common transmitter of such a diverse range of signals, but versatility and molecular constituents of this pathway remain to be determined (35,36).…”

The Chloroplast Triggers Developmental Reprogramming When MUTS HOMOLOG1 Is Suppressed in Plants

“…5A). Alterations in leaf morphology and branching are likely consequences of changes in auxin production and receptor expression (Willige et al, 2011). Effects on flowering and conversion to a perennial growth pattern were associated with changes in the expression of flowering and vernalization regulators (Fornara et al, 2010), including increased FLOWERING LOCUS C SUPPRESSOR OF OVEREXPRESSION OF CO1 (FLC) and decreased SUPPRESSOR OF OVEREXPRESSION OF CO1 (SOC1) expression (Fig.…”

Hormone symphony during root growth and development

“…However, the function of CK is complex, and although the overexpression of CKX in Arabidopsis leads to larger root meristems, CK receptor mutants exhibit short root phenotypes. GA indirectly promotes PIN expression by inhibiting ARR1, and GAs also target PIN proteins for vacuolar degradation (Moubayidin et al, 2010;Willige et al, 2011). The means by which these two processes are stabilized is not clear.…”