Roles of type II H+-PPases and PPsPase1/PECP2 in early developmental stages and PPi homeostasis of Arabidopsis thaliana

Abstract

The regulation of intracellular pyrophosphate (PPi) level is crucial for proper morphogenesis across all taxonomic kingdoms. PPi is released as a byproduct from ~200 metabolic reactions, then hydrolyzed by either membrane-bound (H+-PPase) or soluble pyrophosphatases (PPases). In Arabidopsis, the loss of the vacuolar H+-PPase/FUGU5, a key enzyme in PPi homeostasis, results in delayed growth and a number of developmental defects, pointing to the importance of PPi homeostasis in plant morphogenesis. The Arabidopsis genome encodes several PPases in addition to FUGU5, such as PPsPase1/PECP2, VHP2;1 and VHP2;2, although their significance regarding PPi homeostasis remains elusive. Here, to assess their contribution, phenotypic analyses of cotyledon aspect ratio, palisade tissue cellular phenotypes, adaxial side pavement cell complexity, stomatal distribution, and etiolated seedling length were performed, provided that they were altered due to excess PPi in a fugu5 mutant background. Overall, our analyses revealed that the above five traits were unaffected in ppspase1/pecp2, vhp2;1 and vhp2;2 loss-of-function mutants, as well as in fugu5 mutant lines constitutively overexpressing PPsPase1/PECP2. Furthermore, metabolomics revealed that ppspase1/pecp2, vhp2;1 and vhp2;2 etiolated seedlings exhibited metabolic profiles comparable to the wild type. Together, these results indicate that the contribution of PPsPase1/PECP2, VHP2;1 and VHP2;2 to PPi levels is negligible in comparison to FUGU5 in the early stages of seedling development.

Targeted mutagenesis of the vacuolar H+ translocating pyrophosphatase gene reduces grain chalkiness in rice

“…Most interestingly, vpp5 grains consistently showed reduced chalk (Table 1). Accumulation of PPi, however, causes developmental defects (Tojo et al., 2023). Arabidopsis V‐PPase mutant fugu5 and the RNAi suppression lines display mild to severe growth retardation, which can be rescued by the exogenous supply of sucrose (Ferjani et al., 2011; Pizzio et al., 2015; Segami et al., 2018).…”

Mutations in type II Golgi-localized proton pyrophosphatase AVP2;1/VHP2;1 affect pectic polysaccharide rhamnogalacturonan-II and alter root growth under low boron condition in Arabidopsis thaliana

“…This missense mutation (G800A in CDS) led to an amino acid substitution of glycine to aspartic acid (G267D in protein). G267 is predicted to be located close to the 6th transmembrane domain, and is conserved among AVP1, AVP2;1 and AVP2;2 ( Segami et al., 2010 ; Tojo et al., 2023 ). To examine if the mutant phenotype was because of its mutation in AVP2;1 , two T-DNA lines of AVP2;1 were obtained.…”

“…The introduction of this mutant variant into fugu5-3 rescued shoot growth as when native H + -PPase (AVP1) was introduced (Asaoka et al, 2016), thereby supporting that the hydrolytic role rather than proton pumping of AVP1, is essential for plant growth. On the other hand, Tojo et al (2023) has revealed the negligible contribution of PPi hydrolytic role of AVP2;1 in growth of A. thaliana seedling. This was done by phenotypic characterization of the AVP2;1 mutant, vhp2;1-1/avp2;1-1 (SAIL_512_B02) and fugu5-1vhp2;1-1 double mutant.…”