Long-Distance Movement of Mineral Deficiency-Responsive mRNAs in Nicotiana Benthamiana/Tomato Heterografts

Abstract

Deficiencies in essential mineral nutrients such as nitrogen (N), phosphorus (P), and iron (Fe) severely limit plant growth and crop yield. It has been discovered that both the local sensing system in roots and shoot-to-root systemic signaling via the phloem are involved in the regulation of the adaptive alterations in roots, in response to mineral deficiency. mRNAs are one group of molecules with systemic signaling functions in response to intrinsic and environmental cues; however, the importance of shoot-to-root mobile mRNAs stimulated by low mineral levels is not fully understood. In this study, we established a Nicotiana benthamiana/tomato heterograft system to identify shoot-to-root mobile mRNAs that are produced in response to low N, P or Fe. Multiple long-distance mobile mRNAs were identified to be associated with low mineral levels and a few of them may play important roles in hormonal metabolism and root architecture alteration. A comparison of the mobile mRNAs from our study with those identified from previous studies showed that very few transcripts are conserved among different species.

Keywords: heterograft; long-distance transport; mineral deficiency; mobile mRNA; phloem.

Figure 1

Shoot-to-root mobile mRNAs identified from the N. benthamiana/tomato heterografts grown in a hydroponic condition. (A) No visible phenotypic alterations were observed in the roots of the homograft (left two tall plants) and the heterograft (right three short plants) plants. Bars = 2 cm. (B) Representative heterograft established between N. benthamiana and tomato. The dashed box indicates the graft union (GU). Bars = 2 cm. (C) Venn diagram shows the overlaps and specificities of mobile mRNAs detected in full nutrient and N, P and Fe deficiency conditions. Numbers in the brackets indicated the quantity of mRNAs specifically induced by the individual mineral deficiency.

Figure 2

Venn diagram shows the overlaps and specificities of mobile mRNAs detected in different heterograft systems under mineral deficiency conditions. (A) Comparison of our system with Arabidopsis ecotype grafting under N deficiency condition. (B) Comparison of our system with Arabidopsis ecotype grafting under P deficiency condition. (C) Comparison of our system with cucumber/watermelon heterografting under P deficiency condition.