RNA function and phosphorus use by photosynthetic organisms

Abstract

Phosphorus (P) in RNA accounts for half or more of the total non-storage P in oxygenic photolithotrophs grown in either P-replete or P-limiting growth conditions. Since many natural environments are P-limited for photosynthetic primary productivity, and peak phosphorus fertilizer production is inevitable, the paper analyses what economies in P allocation to RNA could, in principle, increase P-use efficiency of growth (rate of dry matter production per unit organism P). The possibilities of decreasing P allocation to RNA without decreasing growth rate include (1) more widespread down-regulation of RNA production in P-limited organisms, (2) optimal allocation of P to RNA, both spatially among cell compartments and organs, and temporally depending on the stage of growth, and (3) a constant rate of protein synthesis through the diel cycle. Acting on these suggestions would, however, be technically demanding. Keywords: allocation, diel, growth, peptide elongation, protein synthesis INTRODUCTIONRNA is an essential component of all living organisms, and the phosphorus (P) it contains cannot be substituted by any other element. The core role of RNA is in protein synthesis, involving mRNA, rRNA, and tRNA, but it also has (presumably) derived functions in regulation of gene expression. RNA-P is often the major non-storage form of P in photosynthetic organisms, and any attempts to increase the P-use efficiency of growth of algae and plants must include a consideration of economizing on the use of RNA. The paper first deals with the general background of the molecular biology, biochemistry, physiology and biogeochemistry, including optimal allocation of P within the organism in the context of the Growth Rate Hypothesis (Sterner and Elser, 2002). It then considers the various ways of expressing the RNA content of photosynthetic organisms, and the upper limit of the in vivo peptide elongation rate per ribosome. Optimal allocation and the Growth Rate Hypothesis are then revisited in the context of variations in growth rate in relation to RNA content, including temporal and spatial variations in net protein synthesis rate per unit RNA, and then the significance of protein turnover in the total rate of protein synthesis per unit RNA. The paper concludes with consideration of how plant P-use efficiency could be increased by maximizing protein synthesis rate per unit RNA at all times and in all parts of the organism.

Growth rate hypothesis and efficiency of protein synthesis under different sulphate concentrations in two green algae

“…The fact that when microalgae were cultured under P limitation the GRH appeared to hold (Flynn et al . ; Raven cf. Nicklish & Steinberg ) confirms this idea.…”

“…The link between P and growth rate is that most of the non‐storage cell P is in RNA (Sterner & Elser ; Flynn et al . ; Raven ), about 85% of which is ribosomal RNA (rRNA) (Kanda et al . ).…”

“…, ; Flynn et al . ; Loladze & Elser ; Raven ; Daines et al . ), growth rate should be directly related to P supply.…”

“…However, the applicability of this hypothesis to some photosynthetic organisms seems questionable (Flynn et al . ; Raven ). The P cell quota of microalgae varies appreciably (Falkowski et al .…”

Lipid Biosynthesis and Protein Concentration Respond Uniquely to Phosphate Supply during Leaf Development in Highly Phosphorus-Efficient Hakea prostrata

“…Anthocyanin concentrations also increased in these older leaves, which has been suggested to facilitate nutrient resorption by protecting against high radiation levels when chlorophyll levels decline (Hoch et al, 2003;Ougham et al, 2005;Zhang et al, 2013). Given that we were unable to isolate significant amounts of RNA from leaves in these very early stages of senescence, P resorption appears to start with the degradation of rRNA pools, which make up to about 50% of the total organic P fraction in photoautotrophic organisms (Veneklaas et al, 2012;Raven, 2013). In P-limited plants, protein concentrations in senescing leaves were similar to those in mature leaves, despite the large decline in the total RNA pool, indicating slow protein turnover.…”