Contribution of the different omega-3 fatty acid desaturase genes to the cold response in soybean.
ABSTRACT This study analysed the contribution of each omega-3 desaturase to the cold response in soybean. Exposure to cold temperatures (5 °C) did not result in great modifications of the linolenic acid content in leaf membrane lipids. However, an increase in the GmFAD3A transcripts was observed both in plant leaves and soybean cells whereas no changes in GmFAD3B or GmFAD3C expression levels were detected. This increase was reversible and accompanied by the accumulation of an mRNA encoding a truncated form of GmFAD3A (GmFAD3A-T), which originated from alternative splicing of GmFAD3A in response to cold. When the expression of plastidial omega-3 desaturases was analysed, a transient accumulation of GmFAD7-2 mRNA was detected upon cold exposure in mature soybean trifoliate leaves while GmFAD7-1 transcripts remained unchanged. No modification of the GmFAD8-1 and GmFAD8-2 transcripts was observed. The functionality of GmFAD3A, GmFAD3B, GmFAD3C and GmFAD3A-T was examined by heterologous expression in yeast. No activity was detected with GmFAD3A-T, consistent with the absence of one of the His boxes necessary for desaturase activity. The linolenic acid content of Sacharomyces cerevisiae cells overexpressing GmFAD3A or GmFAD3B was higher when the cultures were incubated at cooler temperatures, suggesting that reticular desaturases of the GmFAD3 family, and more specifically GmFAD3A, may play a role in the cold response, even in leaves. The data point to a regulatory mechanism of omega-3 fatty acid desaturases in soybean affecting specific isoforms in both the plastid and the endoplasmic reticulum to maintain appropriate levels of linolenic acid under low temperature conditions.
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ABSTRACT: Primary transcripts (precursor-mRNAs) with introns can undergo alternative splicing to produce multiple transcripts from a single gene by differential use of splice sites, thereby increasing the transcriptome and proteome complexity within and between cells and tissues. Alternative splicing in plants is largely an unexplored area of gene expression, as this phenomenon used to be considered rare. However, recent genome-wide computational analyses have revealed that alternative splicing in flowering plants is far more prevalent than previously thought. Interestingly, pre-mRNAs of many spliceosomal proteins, especially serine/arginine-rich (SR) proteins, are extensively alternatively spliced. Furthermore, stresses have a dramatic effect on alternative splicing of pre-mRNAs including those that encode many spliceosomal proteins. Although the mechanisms that regulate alternative splicing in plants are largely unknown, several reports strongly suggest a key role for SR proteins in spliceosome assembly and regulated splicing. Recent studies suggest that alternative splicing in plants is an important posttranscriptional regulatory mechanism in modulating gene expression and eventually plant form and function.Annual review of plant biology 02/2007; 58:267-94. · 25.96 Impact Factor
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ABSTRACT: For good function, membrane lipids have to be arranged appropriately and be in the correct physical state. In poikilotherms, exposure to cold stress or heat shock can alter membrane properties such that, unless they are corrected quickly, damage and, possibly, death can result. Low temperature stress is countered by modifying membrane lipids such that their average transition temperature is lowered. There are various ways in which this can be achieved but an increase in fatty acid unsaturation is the most common. For heat shock, various changes in lipids have been noted and some defensive strategies involving heat shock proteins noted. In this short review, we will describe recent results where adaptive lipid changes, as a result of temperature stress, have been found. Mechanisms for bringing about such alterations are discussed, together with the contrasting data for different organisms.FEBS Letters 11/2006; 580(23):5477-83. · 3.54 Impact Factor
Article: A Mutation at the fad8 Locus of Arabidopsis Identifies a Second Chloroplast [omega]-3 Desaturase.[show abstract] [hide abstract]
ABSTRACT: Two independently isolated mutations at the fad7 locus in Arabidopsis produced plants with a temperature-conditional phenotype. Leaves of fad7 mutants grown at 28[deg]C contained less than 30% of wild-type levels of trienoic fatty acids (16:3 plus 18:3) compared with more than 70% of wild-type levels for plants grown at 15[deg]C. Screening of an M2 population derived from the fad7-1 line led to the identification of a line, SH1, in which the proportion of trienoic acids was much less than in fad7 plants. The segregation pattern of F2 progeny from a cross between SH1 and wild type indicated that the additional fatty acid mutation in SH1 is at a new locus, designated fad8. In a genetic background that was wild type at the FAD7 locus, the fad8 mutation had no detectable effect on overall leaf fatty acid composition irrespective of the temperature at which plants were grown. However, fatty acid analyses of individual leaf lipids revealed small decreases in the levels of 18:3 in two chloroplast lipids. In fad8 plants grown at 22[deg]C, phospha-tidylglycerol contained 22.5% 18:3 compared with 33.5% in wild-type Arabidopsis. For sulfoquinovosyldiacylglycerol, the values were 31.4 and 44.5%, respectively. Together with information from studies of the cloned FAD8 gene (S. Gibson, V. Arondel, K. Iba, C. Somerville  Plant Physiol 106: 1615-1621), these results indicate that the FAD8 locus encodes a chloroplast-localized 16:2/18:2 desaturase that has a substrate specificity similar to the FAD7 gene product but that is induced by low temperature.Plant physiology 01/1995; 106(4):1609-1614. · 6.53 Impact Factor