SIZ1 regulates phosphate deficiency-induced inhibition of primary root growth of Arabidopsis by modulating Fe accumulation and ROS production in its roots.

Inhibition of primary root (PR) growth is a typical developmental response of Arabidopsis to phosphate (Pi) deficiency. Functional disruption of SIZ1, a SUMO E3 ligase, is known to enhance the Pi deficiency-induced inhibition of PR growth. The molecular mechanism of how SIZ1 regulates PR growth under Pi deficiency, however, remains unknown. SIZ1 was recently reported to partially SUMOylate STOP1, a transcription factor that functions in plant tolerance to aluminum toxicity and in plant responses to Pi deficiency by regulating the expression of encodes an aluminum-activated malate transporter, and its expression is induced by Pi deficiency. In , the expression of is enhanced and the removal of Fe from Pi-deficient medium suppressed the mutant phenotype. In this report, we show that overaccumulates Fe in its root apoplasts, and consequently, produces more hydroxyl radicals, which are detrimental to root growth. Such physiological changes in can be completely suppressed by the mutation of or . Based on previously published work and the results of the current study, we propose that SIZ1 regulates Pi deficiency-mediated PR growth through modulating the accumulation of Fe and the production of hydroxyl radicals by controlling expression.