Cold stress and freezing tolerance negatively affect the fitness of Arabidopsis thaliana accessions under field and controlled conditions

Main conclusion Higher acclimated freezing tolerance improved winter survival, but reduced reproductive fitness of Arabidopsis thaliana accessions under field and controlled conditions. Abstract Low temperature is one of the most important abiotic factors influencing plant fitness and geographical distribution. In addition, cold stress is known to influence crop yield and is therefore of great economic importance. Increased freezing tolerance can be acquired by the process of cold acclimation, but this may be associated with a fitness cost. To assess the influence of cold stress on the fitness of plants, long-term field trials over 5 years were performed with six natural accessions of Arabidopsis thaliana ranging from very tolerant to very sensitive to freezing. Fitness parameters, as seed yield and 1000 seed mass, were measured and correlation analyses with temperature and freezing tolerance data performed. The results were compared with fitness parameters from controlled chamber experiments over 3 years with application of cold priming and triggering conditions. Winter survival and seed yield per plant were positively correlated with temperature in field experiments. In addition, winter survival and 1000 seed mass were correlated with the cold-acclimated freezing tolerance of the selected Arabidopsis accessions. The results provide strong evidence for a trade-off between higher freezing tolerance and reproductive fitness in A. thaliana, which might have ecological impacts in the context of global warming.

OTP970 Is Required for RNA Editing of Chloroplast ndhB Transcripts in Arabidopsis thaliana

RNA editing is essential for compensating for defects or mutations in haploid organelle genomes and is regulated by numerous trans-factors. Pentatricopeptide repeat (PPR) proteins are the prime factors that are involved in RNA editing; however, many have not yet been identified. Here, we screened the plastid-targeted PLS-DYW subfamily of PPR proteins belonging to Arabidopsis thaliana and identified ORGANELLE TRANSCRIPT PROCESSING 970 (OTP970) as a key player in RNA editing in plastids. A loss-of-function otp970 mutant was impaired in RNA editing of ndhB transcripts at site 149 (ndhB-C149). RNA-immunoprecipitation analysis indicated that OTP970 was associated with the ndhB-C149 site. The complementation of the otp970 mutant with OTP970 lacking the DYW domain (OTP970∆DYW) failed to restore the RNA editing of ndhB-C149. ndhB gene encodes the B subunit of the NADH dehydrogenase-like (NDH) complex; however, neither NDH activity and stability nor NDH-PSI supercomplex formation were affected in otp970 mutant compared to the wild type, indicating that alteration in amino acid sequence is not necessary for NdhB function. Together, these results suggest that OTP970 is involved in the RNA editing of ndhB-C149 and that the DYW domain is essential for its function.

SLDP and LIPA mediate lipid droplet-plasma membrane tethering in Arabidopsis thaliana

Membrane contact sites (MCS) are inter-organellar connections that allow for the direct exchange of molecules, such as lipids or Ca2+ between organelles, but can also serve to tether organelles at specific locations within cells. Here we identified and characterised three proteins that form a lipid droplet (LD)-plasma membrane (PM) tethering complex in plant cells, namely LD-localised SEED LD PROTEIN (SLDP) 1 and 2 and PM-localised LD-PLASMA MEMBRANE ADAPTOR (LIPA). Using proteomics and different protein-protein interaction assays, we show that both SLDPs associate with LIPA. Disruption of either SLDP1 and 2 expression, or that of LIPA, leads to an aberrant clustering of LDs in Arabidopsis seedlings. Ectopic co-expression of one of the SLDPs with LIPA on the other hand is sufficient to reconstitute LD-PM tethering in Nicotiana tabacum pollen tubes, a cell type characterised by dynamically moving LDs in the cytosolic streaming. Further, confocal laser scanning microscopy revealed both SLDP2.1 and LIPA to be enriched at LD-PM contact sites in seedlings. These and other results suggest that SLDP and LIPA interact to form a tethering complex that anchors a subset of LDs to the PM during post-germinative seedling growth in Arabidopsis thaliana.

Draft Genome Sequence of Pseudomonas syringae RAYR-BL, a Strain Isolated from Natural Accessions of Arabidopsis thaliana Plants

Here, we report the genome sequence of the P. syringae strain RAYR-BL, isolated from natural accessions of Arabidopsis plants. The draft genome sequence consists of 5.85 Mbp assembled in 110 contigs. The study of P. syringae RAYR-BL is a valuable tool to investigate molecular features of plant-pathogen interaction under environmental conditions.

The Paeonia qiui R2R3-MYB Transcription Factor PqMYB113 Positively Regulates Anthocyanin Accumulation in Arabidopsis thaliana and Tobacco

Paeonia qiui is a wild species of tree peony native to China. Its leaves are purplish red from the bud germination to the flowering stage, and anthocyanin is the main pigment in purplish red leaves. However, the anthocyanin synthesis regulation mechanism in tree peony leaves remains unclear. In this study, an R2R3-MYB, PqMYB113 was identified from the leaves of P. qiui. Phylogenetic analysis revealed that PqMYB113 clustered with Liquidambar LfMYB113 and grape VvMYBA6. Subcellular location analysis showed that PqMYB113 was located in the cell nucleus. The transient reporter assay suggested that PqMYB113 was a transcriptional activator. The overexpression of PqMYB113 in Arabidopsis thaliana and tobacco (Nicotiana tabacum) resulted in increased anthocyanin accumulation and the upregulation of CHS, F3H, F3’H, DFR, and ANS. The dual luciferase reporter assay showed that PqMYB113 could activate the promoters of PqDFR and PqANS. Bimolecular fluorescence complementation assays and yeast two-hybrid assays suggested that PqMYB113 could form a ternary MBW complex with PqbHLH1 and PqWD40 cofactors. These results provide insight into the regulation of anthocyanin biosynthesis in tree peony leaves.