Engineering a sensitive visual‐tracking reporter system for real‐time monitoring phosphorus deficiency in tobacco

Summary Plant phosphorus ( P ) diagnosis is widely used for monitoring P status and guiding P fertilizer application in field conditions. The common methods for predicting plant response to P are time‐ and labour‐consuming chemical measurements of the extractable soil P and plant P concentrations. In this study, we successfully generated a visual reporter system in tobacco ( N icotiana tabacum L .) to monitor plant P status by expressing of a P urple gene ( Pr ) isolated from cauliflower ( B rassica oleracea var botrytis ) driven by the promoter ( P ro) of OsPT6 , a P ‐starvation‐induced rice gene. The leaves of O s PT 6 pro :: P r ( PT 6 pro :: P r) transgenic tobacco continuously turned into dark purple with the increase of duration and severity of P deficiency, and recovered rapidly to basal green colour upon resupply of P . The expression of several anthocyanin biosynthesis involving genes was strongly activated in the transgenic tobacco in comparison to wild type under P ‐deficient condition. Such additive purple colour was not detected by deficiencies of other major‐ and micronutrients or stresses of salt, drought and cold. There was an extremely high correlation between P concentration and anthocyanin accumulation in the transgenic tobacco leaves. Using a hyperspectral sensing technology, P concentration in the leaves of transgenic plants could be predicted by the reflectance spectra at 554 nm wavelength with approximately 0.16 as the threshold value of the P deficiency. Taken together, the colour‐based visual reporter system could be specifically and readily used for monitoring the plant P status by naked eyes and accurately assessed by spectral reflectance.