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The second of two papers in Plant Cell in the last month has just been published. the both describe genes that we cloned from the original Lahner et al. ionomics screen.
This one is "Sphingolipids in the Root Play an Important Role in Regulating the Leaf Ionome in Arabidopsis thaliana". A great collaboration between our group and several groups working on sphingolipids resulted when we landed on a gene in the sphingolipid pathway. Subtly altering the sphingolipid pathway results in what appears to be two different ionomics associated phenotypes: altered suberin and Fe homeostasis.
Here is the abstract of the second paper:
Sphingolipid synthesis is initiated by condensation of Ser with palmitoyl-CoA producing 3-ketodihydrosphinganine (3-KDS), which is reduced by a 3-KDS reductase to dihydrosphinganine. Ser palmitoyltransferase is essential for plant viability. Arabidopsis thaliana contains two genes (At3g06060/TSC10A and At5g19200/TSC10B) encoding proteins with significant similarity to the yeast 3-KDS reductase, Tsc10p. Heterologous expression in yeast of either Arabidopsis gene restored 3-KDS reductase activity to the yeast tsc10Δ mutant, confirming both as bona fide 3-KDS reductase genes. Consistent with sphingolipids having essential functions in plants, double mutant progeny lacking both genes were not recovered from crosses of single tsc10A and tsc10B mutants. Although the 3-KDS reductase genes are functionally redundant and ubiquitously expressed in Arabidopsis, 3-KDS reductase activity was reduced to 10% of wild-type levels in the loss-of-function tsc10a mutant, leading to an altered sphingolipid profile. This perturbation of sphingolipid biosynthesis in the Arabidopsis tsc10a mutant leads an altered leaf ionome, including increases in Na, K, and Rb and decreases in Mg, Ca, Fe, and Mo. Reciprocal grafting revealed that these changes in the leaf ionome are driven by the root and are associated with increases in root suberin and alterations in Fe homeostasis.
And here is a summary intended for lay audiences:
Sphingolipids, a class of membrane lipids with essential functions in all Eukaryotes, are thought to make up a large percentage of some plant membranes and have specific roles in cell processes through the formation of small microdomains. Here we discuss the role of two genes in the sphigolipid biosynthesis pathway in the model plant Arabidopsis Thaliana. When both genes are disrupted, the plants are not viable. However, when the higer expressed gene is disrupted, the plants look normal but elemental profiling reveals that they have significantly altered elemental accumulation in their leaves. Several of the changes appear to be the result of altering the the amount of suberin, a polymer which forms a barrier to water and ion movement in the root, is altered. We also observed alterations in the plants Fe homestasis mechanisms, the cause of which is still unknown. Understanding these processes will enable the prodcution of crops that are more efficient in their water and nutrient uptake effficiency.