The Arabidopsis Mitochondrial Nucleoid-Associated Protein WHIRLY2 Is Required for a Proper Response to Salt Stress.

In the last years, plant organelles have emerged as central coordinators of responses to internal and external stimuli, which can induce stress. Mitochondria play a fundamental role as stress sensors being part of a complex communication network between the organelles and the nucleus. Among the different environmental stresses, salt stress poses a significant challenge and requires efficient signaling and protective mechanisms. By using the why2 T-DNA insertion mutant and a novel knock-out mutant prepared by CRISPR/Cas9-mediated genome editing, this study revealed that WHIRLY2 is crucial for protecting mitochondrial DNA (mtDNA) integrity during salt stress. Loss-of-function mutants show an enhanced sensitivity to salt stress. The disruption of WHIRLY2 causes the impairment of mtDNA repair that results in the accumulation of aberrant recombination products, coinciding with severe alterations in nucleoid integrity and overall mitochondria morphology besides a compromised redox-dependent response and misregulation of antioxidant enzymes. The results of this study revealed that WHIRLY2-mediated structural features in mitochondria (nucleoid compactness and cristae) are important for an effective response to salt stress.

Nitrogen dynamics in soils fertilized with digestate and mineral fertilizers: A full field approach.

Highly stabilized digestate from sewage sludge and digestate-derived ammonium sulphate (RFs), were used in a comparison with synthetic mineral fertilizers (SF) to crop maize in a three-year plot trial in open fields. RFs and SF were dosed to ensure the same amount of mineral N (ammonia-N). In doing so, plots fertilized with digestate received much more N (+185 kg ha-1 of organic N) because digestate also contained organic N. The fate of nitrogen was studied by measuring mineral and organic N in soil at different depths, ammonia and N2O emissions, and N uptake in crops. Soil analyses indicated that at one-meter depth there was no significant difference in nitrate content between RF, SF and Unfertilized plots during crop season indicating that more N dosed with digestate did not lead to extra nitrate leaching. Ammonia emissions and N content in plants and grains measured were also similar for both RF and SF. Measuring denitrification activity by using gene makers resulted in a higher denitrification activity for RF than SF. Nevertheless, N2O measurements showed that SF emitted more N2O than RF (although it was not statistically different) (7.59 ± 3.2 kgN ha-1 for RF and 10.3 ± 6.8 kgN ha-1 for SF), suggesting that probably the addition of organic matter with digestate to RF, increased the denitrification efficiency so that N2 production was favoured. Soil analyses, although were not able detecting N differences between SF and Rf after three years of cropping, revealed a statistical increasing of total carbon, suggesting that dosing digestate lead to carbon (and maybe N) accumulation in soil. Data seem to suggest that N2O/N2 emission and organic N accumulation in soil can explain the fate of the extra N dosed (organic-N) in RF plots.

Bacterial endophytes as indicators of susceptibility to Cercospora Leaf Spot (CLS) disease in Beta vulgaris L.

The fungus Cercospora beticola causes Cercospora Leaf Spot (CLS) of sugar beet (Beta vulgaris L.). Despite the global importance of this disease, durable resistance to CLS has still not been obtained. Therefore, the breeding of tolerant hybrids is a major goal for the sugar beet sector. Although recent studies have suggested that the leaf microbiome composition can offer useful predictors to assist plant breeders, this is an untapped resource in sugar beet breeding efforts. Using Ion GeneStudio S5 technology to sequence amplicons from seven 16S rRNA hypervariable regions, the most recurring endophytes discriminating CLS-symptomatic and symptomless sea beets (Beta vulgaris L.ssp. maritima) were identified. This allowed the design of taxon-specific primer pairs to quantify the abundance of the most representative endophytic species in large naturally occurring populations of sea beet and subsequently in sugar beet breeding genotypes under either CLS symptomless or infection stages using qPCR. Among the screened bacterial genera, Methylobacterium and Mucilaginibacter were found to be significantly (p < 0.05) more abundant in symptomatic sea beets with respect to symptomless. In cultivated sugar beet material under CLS infection, the comparison between resistant and susceptible genotypes confirmed that the susceptible genotypes hosted higher contents of the above-mentioned bacterial genera. These results suggest that the abundance of these species can be correlated with increased sensitivity to CLS disease. This evidence can further prompt novel protocols to assist plant breeding of sugar beet in the pursuit of improved pathogen resistance.

SNP Alleles Associated With Low Bolting Tendency in Sugar Beet.

The identification of efficient molecular markers related to low bolting tendency is a priority in sugar beet (Beta vulgaris L.) breeding. This study aimed to identify SNP markers associated with low bolting tendency by establishing a genome-wide association study. An elaborate 3-year field trial comprising 13 sugar beet lines identified L14 as the one exhibiting the lowest bolting tendency along with an increased survival rate after autumnal sowing. For SNP discovery following phenotyping, contrasting phenotypes of 24 non-bolting and 15 bolting plants of the L14 line were sequenced by restriction site-associated DNA sequencing (RAD-seq). An association model was established with a set of 10,924 RAD-based single nucleotide polymorphism (SNP) markers. The allelic status of the most significantly associated SNPs ranked based on their differential allelic status between contrasting phenotypes (p < 0.01) was confirmed on three different validation datasets comprising diverse sugar beet lines and varieties adopting a range of SNP detection technologies. This study has led to the identification of SNP_36780842 and SNP_48607347 linked to low bolting tendency and can be used for marker-assisted breeding and selection in sugar beet.

Novel Effects of Leonardite-Based Applications on Sugar Beet.

The present study aimed to explore the effects of foliar application of a leonardite-based product on sugar beet (Beta vulgaris L.) plants grown in the field. The approach concerned the evaluation of the community compositional structure of plant endophytic bacteria through a metabarcoding approach, the expression level of a gene panel related to hormonal metabolism and signaling, and the main sugar beet productivity traits. Results indicated that plants treated with leonardite (dosage of 2,000 ml ha-1, dilution 1:125, 4 mg C l-1) compared with untreated ones had a significant increase (p < 0.05) in (i) the abundance of Oxalicibacterium spp., recognized to be an endophyte bacterial genus with plant growth-promoting activity; (ii) the expression level of LAX2 gene, coding for auxin transport proteins; and (iii) sugar yield. This study represents a step forward to advance our understanding of the changes induced by leonardite-based biostimulant in sugar beet.