An analysis of seed longevity in Arabidopsis using modifiers of seed maturation mutants

Seeds ensure the survival of most land plant species and the conservation of their unique genetic resources. Seed longevity is a quantitative trait that depends on environmental conditions during formation, harvest and storage of seeds and on structures, macromolecules and chemical compounds that protect the embryo. Seed longevity is consequently a complex genetic trait to dissect. Its study requires the identification of factors that result in an improvement or in a reduction of seed longevity. Wild-type seeds of the model plant Arabidopsis remain viable for several years, which makes the study of longevity a time consuming process. An approach to overcome this problem makes use of the seed developmental mutants abi3-5 and lec1-3, that cause rapid seed deterioration. These mutants provide a sensitized genetic background in which the effects of genes influencing longevity can be faster evaluated. The Arabidopsis natural variation for longevity was exploited by crossing several Arabidopsis accessions with abi3-5 and lec1-3 mutants and subsequent selection of lines with improved longevity in the progeny. As a result, various introgression lines carrying natural modifiers alleles were identified. The three natural modifier lines with the strongest effects were selected. One had an introgression of the Seis am Schlern accession in abi3-5 background and two had different introgressions of the Shahdara accession in lec1-3 background. These lines were backcrossed with abi3-5 or lec1-3 to reduce the contribution of wild-type accession�s genome and to map the modifiers. The seed proteome profiles of modifier and mutant lines were studied in relation to longevity. This analysis revealed that the two modifiers from Shahdara could activate the expression of most seed storage proteins in a LEC1-independent way. In addition, four abi3-5 suppressor mutants derived from a mutagenesis screen were studied. In these lines the level of oxidative damage was correlated with seed longevity. The strongest suppressor, suppressor of abi3-5 (sua), reverted all of the abi3-5 mutant phenotypes. Fine mapping and map based cloning revealed that SUA encodes an RNA binding protein. Interestingly, sua only suppressed the abi3-5 allele but did not affect other abi3 alleles. Immunological analysis revealed that abi3-5 seeds contain a truncated abi3 protein which is restored to nearly full length ABI3 protein in the sua abi3-5 double mutant. Analysis of transcripts revealed that the sua mutation causes the splicing of a cryptic intron in ABI3 and the accumulation of a splice variant that repairs the abi3-5 mutation and results in a shorter but functional version of the ABI3 protein. The SUA gene is not directly implicated in seed longevity, but participates in mRNA metabolism processes

The Conserved Splicing Factor SUA Controls Alternative Splicing of the Developmental Regulator ABI3 in Arabidopsis[W][OA]

The Arabidopsisgene ABI3 shows developmentally regulated alternative splicing. ABI3-α and ABI3-β splice variants encode full-length and truncated ABI3 proteins, respectively. The conserved splicing factor SUA reduces splicing of a cryptic ABI3 intron, which leads to the accumulation of ABI3-α. Mutations in sua suppress the frameshift mutant abi3-5 by restoring its reading frame

An Ancient Bacterial Signaling Pathway Regulates Chloroplast Function to Influence Growth and Development in Arabidopsis.

International audienceThe chloroplast originated from the endosymbiosis of an ancient photosynthetic bacterium by a eukaryotic cell. Remarkably, the chloroplast has retained elements of a bacterial stress response pathway that is mediated by the signaling nucleotides guanosine penta- and tetraphosphate (ppGpp). However, an understanding of the mechanism and outcomes ofppGppsignaling in the photosynthetic eukaryotes has remained elusive. Using the model plantArabidopsis thaliana, we show thatppGppis a potent regulator of chloroplast gene expression in vivo that directly reduces the quantity of chloroplast transcripts and chloroplast-encoded proteins. We then go on to demonstrate that the antagonistic functions of different plant RelA SpoT homologs together modulateppGpplevels to regulate chloroplast function and show that they are required for optimal plant growth, chloroplast volume, and chloroplast breakdown during dark-induced and developmental senescence. Therefore, our results show thatppGppsignaling is not only linked to stress responses in plants but is also an important mediator of cooperation between the chloroplast and the nucleocytoplasmic compartment during plant growth and development

Guanosine tetraphosphate modulates salicylic acid signalling and the resistance of Arabidopsis thalianaArabidopsis\ thaliana to Turnip mosaic virus

International audienceChloroplasts can act as key players in the perception and acclimatization of plants to incoming environmental signals. A growing body of evidence indicates that chloroplasts play a critical role in plant immunity. Chloroplast function can be regulated by the nucleotides guanosine tetraphosphate and pentaphosphate [(p)ppGpp]. In plants, (p)ppGpp levels increase in response to abiotic stress and to plant hormones which are involved in abiotic and biotic stress signalling. In this study, we analysed the transcriptome of Arabidopsis plants that over‐accumulate (p)ppGpp, and unexpectedly found a decrease in the levels of a broad range of transcripts for plant defence and immunity. To determine whether (p)ppGpp is involved in the modulation of plant immunity, we analysed the susceptibility of plants with different levels of (p)ppGpp to Turnip mosaic virus (TuMV) carrying a green fluorescent protein (GFP) reporter. We found that (p)ppGpp accumulation was associated with increased susceptibility to TuMV and reduced levels of the defence hormone salicylic acid (SA). In contrast, plants with lower (p)ppGpp levels showed reduced susceptibility to TuMV, and this was associated with the precocious up‐regulation of defence‐related genes and increased SA content. We have therefore demonstrated a new link between (p)ppGpp metabolism and plant immunity in Arabidopsis