Phosphate deficiency activates autophagy in the root

Scientists of the Department Molecular Signal Processing have shown that plants grown under phosphate deficiency trigger stress-induced autophagy processes in their root tips. Until now, processes of autophagous self-digestion in plant cells were only known in cases of nitrogen, carbon or sulphur deficiency, but not under phosphate limitation. In their recent publication in Plant Physiology, plant researchers of the IPB show that the increased formation of autophagosomes under phosphate deficiency in the root apex is initiated by general stress reactions of the endoplasmic reticulum (ER).

Triggering of ER stress seems to be directly related to the perception of phosphate availability in the soil. In case of nitrogen or carbon hunger, stress-induced autophagy primarily serves to recycle the limited nutrients. However, this could not be shown for phosphate deficiency. Rather, it was found that the adaptation to phosphate limitation, which results in accumulation of iron ions, formation of reactive oxygen species, and a local cell wall thickening in the stem cell niche, leading to a stop of deep growth of root apex and an increased formation of lateral roots, induces ER stress-related autophagy.

The LPR1 and PDR2 genes play an important role in this fundamental change in the root architecture under phosphate deficiency. LPR1, a cell wall localized ferroxidase, has an activating effect on ER stress-related formation of autophagosomes. Ferroxidase is regulated by PDR2 by a previously unknown mechanism. PDR2 encodes a P5-ATPase in the ER. Its substrate and thus its function are yet unknown. The study showed that a loss of the P5-ATPase leads to an increased stress-induced autophagy under phosphate deficiency. In addition to heat and chemical stressors, phosphate deficiency was identified for the first time as a natural trigger for ER-stress autophagy. The findings resulted in a first model.

Publication:
Christin Naumann, Jens Müller, Siriwat Sakhonwasee, Annika Wieghaus, Gerd Hause, Marcus Heisters, Katharina Bürstenbinder & Steffen Abel. The local phosphate deficiency response activates ER Stress-dependent autophagy. Published December 2018 in Plant Physiology, DOI: https://doi.org/10.1104/pp.18.01379