No abstract

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.

OsABCG36 localized at the plasma membrane functions as an efflux transporter for Cd or Cd conjugates in the roots, and is involved in Cd tolerance in rice.

We used cDNA microarrays containing ~9,000 unigenes to identify 486 salt responsive expressed sequence tags (ESTs) (representing ~450 unigenes) in shoots of the highly salt-tolerant rice variety, Nona Bokra (Oryza sativa L. ssp. Indica pv. Nona). Some of the genes identified in this study had previously been associated with salt stress. However the majority were novel, indicating that there is a great number of genes that are induced by salt exposure. Analysis of the salt stress expression profile data of Nona provided clues regarding some putative cellular and molecular processes that are undertaken by this tolerant rice variety in response to salt stress. Namely, we found that multiple transcription factors were induced during the initial salt response of shoots. Many genes whose encoded proteins are implicated in detoxification, protectant and transport were rapidly induced. Genes supporting photosynthesis were repressed and those supporting carbohydrate metabolism were altered. Commonality among the genes induced by salt exposure with those induced during senescence and biotic stress responses suggests that there are shared signaling pathways among these processes. We further compared the transcriptome changes of the salt-sensitive cultivar, IR28, with that of Nona rice. Many genes that are salt responsive in Nona were found to be differentially regulated in IR28. This study identified a large number of candidate functional genes that appear to be involved in salt tolerance and further examination of these genes may enable the molecular basis of salt tolerance to be elucidated.