Caitlin Cridland

Inorganic phosphate (P i ), while indispensable for all biological organisms and a major agricultural macronutrient, is an increasingly limited and nonrenewable resource. Recent studies demonstrate the importance of inositol pyrophosphates (PP-InsPs) in plant P i signaling and homeostasis, however the extent to which PP-InsPs impact plant development is not well understood. We report that transgenic expression of the Saccharomyces cerevisiae enzyme Diadenosine and Diphosphoinositol Polyphosphate Phosphohydrolase (DDP1) in Arabidopsis thaliana and Thlaspi arvense (pennycress) provide a unique translational utility for P i phytoremediation as well as unique germplasm and insight on the long-term impacts of reduced PP-InsPs. Transgenic DDP1 expression in Arabidopsis decreased PP-InsPs, impacted growth and development, and increased P i accumulation leading to P i toxicity. Analysis of P i Starvation Response (PSR) marker genes indicated that the PSR is activated in DDP1 expressing plants. We assessed translational utility through transformation of pennycress, a spring annual cover crop with emerging importance as a biofuel crop, with a DDP1 transgene. Pennycress plants expressing DDP1 showed similar altered P i accumulation phenotypes, suggesting that these plants could potentially serve to remove P i from P i -rich soils. Our study addresses the long-term impacts of PP-InsP reduction on plant growth, as well as establishing a starting material for a unique P i reclaiming cover crop. SIGNIFICANCE STATEMENT: A major challenge to food security is the phosphorus (P) crisis. A global P shortage is imminent based on the misuse of current resources and will be further aggravated by climate change and a lack of policy addressing sustainability. Our work addresses this crisis by investigating the sustained impact of altering inositol pyrophosphates to manipulate plant P accumulation, a strategy that could be used to remediate nutrient-polluted environments.

Phosphate is a major plant macronutrient and low phosphate availability severely limits global crop productivity. In Arabidopsis, a key regulator of the transcriptional response to low phosphate, phosphate starvation response 1 (PHR1), is modulated by a class of signaling molecules called inositol pyrophosphates (PP-InsPs). Two closely related diphosphoinositol pentakisphosphate enzymes (AtVIP1 and AtVIP2) are responsible for the synthesis and turnover of InsP₈, the most implicated molecule. This study is focused on characterizing Arabidopsis vip1/vip2 double mutants and their response to low phosphate. We present evidence that both local and systemic responses to phosphate limitation are dampened in the vip1/vip2 mutants as compared to wild-type plants. Specifically, we demonstrate that under Pi-limiting conditions, the vip1/vip2 mutants have shorter root hairs and lateral roots, less accumulation of anthocyanin and less accumulation of sulfolipids and galactolipids. However, phosphate starvation response (PSR) gene expression is unaffected. Interestingly, many of these phenotypes are opposite to those exhibited by other mutants with defects in the PP-InsP synthesis pathway. Our results provide insight on the nexus between inositol phosphates and pyrophosphates involved in complex regulatory mechanisms underpinning phosphate homeostasis in plants.

Like many institutions around the world, the COVID‐19 pandemic prompted us to shift our summer 2020 in‐person undergraduate experiential learning program to a remote, virtual format. Here, we present our observations, summarized in 10 best practices, for moving a STEM‐focused research experience for undergraduates, experiential learning program or research‐based course online. We will also discuss how our program was originally designed and implemented, and how we adapted our activities to deliver an at‐home research experience that maintained student engagement, mentorship, and a shared sense of community.

The ability of an organism to maintain homeostasis in changing conditions is crucial for growth and survival. Eukaryotes have developed complex signaling pathways to adapt to a readily changing environment, including the inositol phosphate (InsP) signaling pathway. In plants and humans the pyrophosphorylated inositol molecules, inositol pyrophosphates (PP-InsPs), have been implicated in phosphate and energy sensing. PP-InsPs are synthesized from the phosphorylation of InsP₆, the most abundant InsP. The plant PP-InsP synthesis pathway is similar but distinct from that of the human, which may reflect differences in how molecules such as Ins(1,4,5)P₃ and InsP₆ function in plants vs. animals. In addition, PP-InsPs can potentially interact with several major signaling proteins in plants, suggesting PP-InsPs play unique signaling roles via binding to protein partners. In this review, we will compare the biosynthesis and role of PP-InsPs in animals and plants, focusing on three central themes: InsP₆ synthesis pathways, synthesis and regulation of the PP-InsPs, and function of a specific protein domain called the Syg1, Pho1, Xpr1 (SPX ) domain in binding PP-InsPs and regulating inorganic phosphate (Pi) sensing. This review will provide novel insights into the biosynthetic pathway and bioactivity of these key signaling molecules in plant and human systems.