Recent advances in unraveling the mystery of combined nutrient stress in plants

Soil Analysis by Mobile Multinuclear NMR: Quantification of Phosphorus, Aluminum, and Sodium

Soil analyses are essential to ensure economically and environmentally sustainable crop production while maintaining the soil fertile for future use. Unfortunately, common soil analyses may be highly demanding in terms of time, chemicals, and costs. This applies, in particular, when total quantities of elements are desired. As an easy and fast alternative without consumption of chemicals, we here present mobile 31P, 27Al, 23Na, and 1H NMR for quantification of phosphorus, aluminum, and sodium contents in soil. This enables accurate on-site analysis and is suitable for direct measurement on fresh, undried soil samples since the water content is quantified as well. For demonstration, 40 various Danish agricultural soil samples were analyzed using a mobile NMR sensor, and the results were compared with external laboratory analyses for P, Al, and Na. The laboratory analyses were conducted with ICP-OES after four-acid digestion, which additionally were compared with aqua regia digestion, showing inadequacies in the performance of the latter. Good agreement between NMR and laboratory analyses (correlation coefficients 0.91 for P, 0.98 for Al, and 0.90 for Na, in the concentration ranges 250-1200 ppm P, 1.4-5% Al, and 0.3-1% Na) were obtained with high accuracy using NMR measuring times of 20 min to 1 h for P, 4-12 min for Al, and 6-20 min for Na. Additionally, the NMR measurements provide information on the amount of P associated with paramagnetic centers (e.g., Fe3+). Good correlations were also observed to other parameters such as the clay content, which is predictable from the intensity of the more fast-relaxing of three 27Al NMR components.

PDR9 allelic variation and MYB63 modulate nutrient-dependent coumarin homeostasis in Arabidopsis

Plant roots release phytochemicals into the soil environment to influence nutrient availability and uptake. Arabidopsis thaliana roots release phenylpropanoid coumarins in response to iron (Fe) deficiency, likely to enhance Fe uptake and improve plant health. This response requires sufficient phosphorus (P) in the root environment. Nonetheless, the regulatory interplay influencing coumarin production under varying availabilities of Fe and P is not known. Through genome-wide association studies, we have pinpointed the influence of the ABC transporter G family member, PDR9, on coumarin accumulation and trafficking (homeostasis) under combined Fe and P deficiency. We show that genetic variation in the promoter of PDR9 regulates its expression in a manner associated with coumarin production. Furthermore, we find that MYB63 transcription factor controls dedicated coumarin production by regulating both COUMARIN SYNTHASE (COSY) and FERULOYL-CoA 6'-HYDROXYLASE 1 (F6'H1) expression while orchestrating secretion through PDR9 genes under Fe and P combined deficiency. This integrated approach illuminates the intricate connections between nutrient signaling pathways in coumarin response mechanisms.