Rapid induction of regulatory and transporter genes in response to phosphorus, potassium, and iron deficiencies in tomato roots. Evidence for cross talk and root/rhizosphere-mediated signals

Mineral nutrient deficiencies constitute major limitations for plant growth on agricultural soils around the world. To identify genes that possibly play roles in plant mineral nutrition, we recently generated a high-density array consisting of 1,280 genes from tomato (Lycopersicon esculentum) roots for expression profiling in nitrogen (N) nutrition. In the current study, we used the same array to search for genes induced by phosphorus (P), potassium (K+), and iron (Fe) deficiencies. RNA gel-blot analysis was conducted to study the time-dependent kinetics for expression of these genes in response to withholding P, K, or Fe. Genes previously not associated with P, K, and Fe nutrition were identified, such as transcription factor, mitogen-activated protein (MAP) kinase, MAP kinase kinase, and 14-3-3 proteins. Many of these genes were induced within 1 h after withholding the specific nutrient from roots of intact plants; thus, RNA gel-blot analysis was repeated for specific genes (transcription factor and MAP kinase) in roots of decapitated plants to investigate the tissue-specific location of the signal triggering gene induction. Both genes were induced just as rapidly in decapitated plants, suggesting that the rapid response to the absence of P, K, or Fe in the root-bathing medium is triggered either by a root-localized signal or because of root sensing of the mineral environment surrounding the roots. We also show that expression of Pi, K, and Fe transporter genes were up-regulated by all three treatments, suggesting coordination and coregulation of the uptake of these three essential mineral nutrients.