Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 29, 2002
Publication Date: May 20, 2003
Citation: WANG, Y.H., KOCHIAN, L.V., DOYLE, J.J., GARVIN, D.F. TWO TOMATO NON-SYMBIOTIC HAEMOGLOBIN GENES ARE DIFFERENTIALLY EXPRESSED IN RESPONSE TO DIVERSE CHANGES IN MINERAL NUTRIENT STATUS. PLANT CELL AND ENVIRONMENT. 2003. V. 26. P. 673-680. Interpretive Summary: Plants obtain the vast majority of their nutrients from the soil, and agricultural production relies heavily on the application of nutrient fertilizers. It would be desirable to develop crops with a reduced dependence on fertilizers. An in-depth understanding of the cellular events that lead to increased nutrient acquisition will identify new potential avenues for developing crops that require less fertilizer. To date, a role for plant proteins called nonsymbiotic hemoglobins has yet to be established. In this study, we characterized two tomato genes encoding nonsymbiotic hemoglobins and examined how these genes respond to changes in nutrient status. The two tomato genes exhibit differences in their patterns of expression throughout the plant, and both are expressed continuously in roots. However, the two genes exhibit dramatic differences in responsiveness to nutrient status. Only one of the genes exhibited a rapid increase in expression in response to all four modifications in nutrient status, including those involving the three principal components of fertilizers (phosphorus, potassium, nitrogen), as well as iron. These results suggest a previously unrecognized broad role for nonsymbiotic hemoglobins in cellular events associated with enhanced nutrient acquisition. Such new insights into the events associated with increased nutrient uptake are ultimately expected to prove useful for enhancing the capacity of plants to use nutrients that they obtain from the soil. By doing so, on-farm fertilizer expenditures will decrease, and the environmental damage caused by fertilizer run-off will also be reduced.
Technical Abstract: The role of plant nonsymbiotic hemoglobins remains undefined, but recent findings have emerged that suggest a possible role in plant nutrition. In this study, two tomato (Lycopersicon esculentum L.) nonsymbiotic hemoglobin cDNAs have been characterized and studies undertaken to evaluate the relationship between nutrient status and expression of these two genes. The etranslation products of these two genes, LeHb1 and LeHb2, are only 55% identical. LeHb1 mRNA is present in highest abundance in roots and immature fruits, and in decreasing abundance in stems, leaves, and flowers, while LeHb2 expression is similar across tissues except in leaves, where it is lower. Hydroponic culture was used to evaluate the response of these two genes to modifications in nutrient status. LeHb1 expression increased rapidly in roots in response to every nutrient treatment examined in hydroponic culture, including removal of phosphate, potassium, or iron from mthe solution culture medium, as well as by supplying nitrate to the medium In contrast, LeHb2 expression was not significantly altered in response to these same treatments. These results are the first demonstration that nonsymbiotic hemoglobin gene expression is influenced by a broad range of changes both in mineral macronutrient and micronutrient status, suggesting a previously unrecognized generic role for nonsymbiotic hemoglobins in the processes that maintain mineral nutrient homeostasis in plants.