Keep an Eye on PPi: The Vacuolar-Type H+-Pyrophosphatase Regulates Postgerminative Development in Arabidopsis[C][W][OA]

Oilseed germination requires gluconeogenesis, the conversion of storage lipids into carbohydrates, to sustain seedling heterotrophic growth. Pyrophosphate (PPi), a byproduct of ATP hydrolysis, is released by active metabolism in imbibed seeds. We report that the removal of PPi by plant vacuolar H+-pyrophosphatase is central for successful gluconeogenesis and resumption of postembryonic growth

Transcriptional activation of auxin biosynthesis drives developmental reprogramming of differentiated cells

Abstract Plant cells exhibit remarkable plasticity of their differentiation states, enabling regeneration of whole plants from differentiated somatic cells. How they revert cell fate and express pluripotency, however, remains unclear. In this study, we demonstrate that transcriptional activation of auxin biosynthesis is crucial for reprogramming differentiated Arabidopsis (Arabidopsis thaliana) leaf cells. Our data show that interfering with the activity of histone acetyltransferases dramatically reduces callus formation from leaf mesophyll protoplasts. Histone acetylation permits transcriptional activation of PLETHORAs, leading to the induction of their downstream YUCCA1 gene encoding an enzyme for auxin biosynthesis. Auxin biosynthesis is in turn required to accomplish initial cell division through the activation of G2/M phase genes mediated by MYB DOMAIN PROTEIN 3-RELATED (MYB3Rs). We further show that the AUXIN RESPONSE FACTOR 7 (ARF7)/ARF19 and INDOLE-3-ACETIC ACID INDUCIBLE 3 (IAA3)/IAA18-mediated auxin signaling pathway is responsible for cell cycle reactivation by transcriptionally upregulating MYB3R4. These findings provide a mechanistic model of how differentiated plant cells revert their fate and reinitiate the cell cycle to become pluripotent.</jats:p

Regulation of pyrophosphate levels by H+-PPase is central for proper resumption of early plant development

The synthesis of DNA, RNA, and de novo proteins is fundamental for early development of the seedling after germination, but such processes release pyrophosphate (PPi) as a byproduct of ATP hydrolysis. The over-accumulation of the inhibitory metabolite PPi in the cytosol hinders these biosynthetic reactions. All living organisms possess ubiquitous enzymes collectively called inorganic pyrophosphatases (PPases), which catalyze the hydrolysis of PPi into two orthophosphate (Pi) molecules. Defects in PPase activity cause severe developmental defects and/or growth arrest in several organisms. In higher plants, a proton-translocating vacuolar PPase (H+­PPase) uses the energy of PPi hydrolysis to acidify the vacuole. However, the biological implications of PPi hydrolysis are vague due to the widespread belief that the major role of H+­PPase in plants is vacuolar acidification. We have shown that the Arabidopsis fugu5 mutant phenotype, caused by a defect in H+­PPase activity, is rescued by complementation with the yeast cytosolic PPase IPP1. In addition, our analyses have revealed that increased cytosolic PPi levels impair postgerminative development in fugu5 by inhibiting gluconeogenesis. This led us to the conclusion that the role of H+­PPase as a proton-pump is negligible. Here, we present further evidence of the growth-boosting effects of removing PPi in later stages of plant vegetative development, and briefly discuss the biological role of PPases and their potential applications in different disciplines and in various organisms