Changes in flavonol content and transcript levels of genes in the flavonoid pathway in tobacco under phosphorus deficiency

Inorganic phosphorus (Pi) is an essential macronutrient for plant growth and development. An imbalance of Pi in plants greatly affects secondary metabolic pathways, including the flavonoid biosynthetic pathway. Flavonols and anthocyanins are the two main products of the flavonoid biosynthetic pathway. In this study, we analyzed the physiological and molecular changes in tobacco plants under Pi deficiency during the vegetative growth phase. A deficiency of Pi resulted in the accumulation of flavonols, but not anthocyanins, in leaves. Quantitative reverse transcription polymerase chain reaction analyses showed that the transcript levels of five genes involved in flavonol biosynthesis, namely, NtCHS, NtCHI, NtF3H, NtF3′H, and NtFLS, were increased in leaves under Pi deficiency. In contrast, the transcript level of the gene encoding dihydroflavonol 4-reductase (NtDFR), a key gene in anthocyanidin biosynthesis, was not increased under Pi deficiency. We detected upregulated transcription of NtAN2, a regulatory gene upstream of NtDFR, under Pi deficiency. Our results show that tobacco plants accumulate flavonols, but not anthocyanins, under Pi deficiency. One reason for the inactivation of anthocyanin biosynthesis in leaves of Pi-deficient tobacco could be that NtAN2 requires other transcription factor(s) for its activation.