Inorganic phosphate (Pi) and Zinc (Zn) are essential nutrients for normal plant growth. Interaction between these elements has been observed in many crop plants. Despite its agronomic importance, the biological significance and genetic basis of this interaction remain largely unknown. Here we examined the Pi/Zn interaction in two lettuce (Lactuca sativa) varieties, namely, “Paris Island Cos” and “Kordaat.” The effects of variation in Pi and Zn supply were assessed on biomass and photosynthesis for each variety. Paris Island Cos displayed better growth and photosynthesis compared to Kordaat under all the conditions tested. Correlation analysis was performed to determine the interconnectivity between Pi and Zn intracellular contents in both varieties. Paris Island Cos showed a strong negative correlation between the accumulation levels of Pi and Zn in shoots and roots. However, no relation was observed for Kordaat. The increase of Zn concentration in the medium causes a decrease in dynamics of Pi transport in Paris Island Cos, but not in Kordaat plants. Taken together, results revealed a contrasting behavior between the two lettuce varieties in terms of the coregulation of Pi and Zn homeostasis and provided evidence in favor of a genetic basis for the interconnection of these two elements.

Phytic acid (PA) is the main phosphorus storage form in plant seeds. It is recognized as an anti-nutrient for humans and non-ruminant animals, as well as one of the major sources of phosphorus that contributes to eutrophication. Therefore, engineering plants with low PA content without affecting plant growth capacity has become a major focus in plant breeding. Nevertheless, lack of knowledge on the role of PA seed reserves in regulating plant growth and in maintaining ion homeostasis hinders such an agronomical application. In this context, we report here that the over-expression of the bacterial phytase PHY-US417 in Arabidopsis leads to a significant decrease in seed PA, without any effect on the seed germination potential. Interestingly, this over-expression also induced a higher remobilization of free iron during germination. Moreover, the PHY-over-expressor lines show an increase in inorganic phosphate and sulfate contents, and a higher biomass production after phosphate starvation. Finally, phosphate sensing was altered because of the changes in the expression of genes induced by phosphate starvation or involved in phosphate or sulfate transport. Together, these results show that the over-expression of PHY-US417 reduces PA concentration, and provide the first evidence for the involvement of PA in the regulation of sulfate and phosphate homeostasis and signaling.