The SCL30a SR protein regulates ABA-dependent seed traits and germination under stress.

SR proteins are conserved RNA-binding proteins best known as splicing regulators that have also been implicated in other steps of gene expression. Despite mounting evidence for a role in plant development and stress responses, the molecular pathways underlying SR protein regulation of these processes remain poorly understood. Here we show that the plant-specific SCL30a SR protein negatively regulates ABA signaling to control seed traits and stress responses during germination in Arabidopsis. Transcriptome-wide analyses revealed that loss of SCL30a function barely affects splicing, but largely induces ABA-responsive gene expression and genes repressed during germination. Accordingly, scl30a mutant seeds display delayed germination and hypersensitivity to ABA and high salinity, while transgenic plants overexpressing SCL30a exhibit reduced ABA and salt stress sensitivity. An ABA biosynthesis inhibitor rescues the enhanced mutant seed stress sensitivity, and epistatic analyses confirm that this hypersensitivity requires a functional ABA pathway. Finally, seed ABA levels are unchanged by altered SCL30a expression, indicating that the gene promotes seed germination under stress by reducing sensitivity to the phytohormone. Our results reveal a new player in ABA-mediated control of early development and stress response.

Oil and protein accumulation in developing seeds is influenced by the expression of a cytosolic pyrophosphatase in Arabidopsis.

This study describes a dominant low-seed-oil mutant (lo15571) of Arabidopsis (Arabidopsis thaliana) generated by enhancer tagging. Compositional analysis of developing siliques and mature seeds indicated reduced conversion of photoassimilates to oil. Immunoblot analysis revealed increased levels of At1g01050 protein in developing siliques of lo15571. At1g01050 encodes a soluble, cytosolic pyrophosphatase and is one of five closely related genes that share predicted cytosolic localization and at least 70% amino acid sequence identity. Expression of At1g01050 using a seed-preferred promoter recreated most features of the lo15571 seed phenotype, including low seed oil content and increased levels of transient starch and soluble sugars in developing siliques. Seed-preferred RNA interference-mediated silencing of At1g01050 and At3g53620, a second cytosolic pyrophosphatase gene that shows expression during seed filling, led to a heritable oil increase of 1% to 4%, mostly at the expense of seed storage protein. These results are consistent with a scenario in which the rate of mobilization of sucrose, for precursor supply of seed storage lipid biosynthesis by cytosolic glycolysis, is strongly influenced by the expression of endogenous pyrophosphatase enzymes. This emphasizes the central role of pyrophosphate-dependent reactions supporting cytosolic glycolysis during seed maturation when ATP supply is low, presumably due to hypoxic conditions. This route is the major route providing precursors for seed oil biosynthesis. ATP-dependent reactions at the entry point of glycolysis in the cytosol or plastid cannot fully compensate for the loss of oil content observed in transgenic events with increased expression of cytosolic pyrophosphatase enzyme in the cytosol. These findings shed new light on the dynamic properties of cytosolic pyrophosphate pools in developing seed and their influence on carbon partitioning during seed filling. Finally, our work uniquely demonstrates that genes encoding cytosolic pyrophosphatase enzymes provide novel targets to improve seed composition for plant biotechnology applications.

A novel omega3-fatty acid desaturase involved in the biosynthesis of eicosapentaenoic acid.

Long-chain n-3 PUFAs (polyunsaturated fatty acids) such as EPA (eicosapentaenoic acid; 20:5 n-3) have important therapeutic and nutritional benefits in humans. In plants, cyanobacteria and nematodes, omega3-desaturases catalyse the formation of these n-3 fatty acids from n-6 fatty acid precursors. Here we describe the isolation and characterization of a gene ( sdd17 ) derived from an EPA-rich fungus, Saprolegnia diclina, that encodes a novel omega3-desaturase. This gene was isolated by PCR amplification of an S. diclina cDNA library using oligonucleotide primers corresponding to conserved regions of known omega3-desaturases. Expression of this gene in Saccharomyces cerevisiae, in the presence of various fatty acid substrates, revealed that the recombinant protein could exclusively desaturate 20-carbon n-6 fatty acid substrates with a distinct preference for ARA (arachidonic acid; 20:4 n-6), converting it into EPA. This activity differs from that of the known omega3-desaturases from any organism. Plant and cyanobacterial omega3-desaturases exclusively desaturate 18-carbon n-6 PUFAs, and a Caenorhabditis elegans omega3-desaturase preferentially desaturated 18-carbon PUFAs over 20-carbon substrates, and could not convert ARA into EPA when expressed in yeast. The sdd17 -encoded desaturase was also functional in transgenic somatic soya bean embryos, resulting in the production of EPA from exogenously supplied ARA, thus demonstrating its potential for use in the production of EPA in transgenic oilseed crops.