Estimation of Stomatal Aperture in Arabidopsis thaliana Using Silicone Rubber Imprints

HD2A and HD2C co-regulate drought stress response by modulating stomatal closure and root growth in Arabidopsis

Histone deacetylase 2 (HD2) is a unique family of histone deacetylases (HDACs) in plants. Despite evidence that certain HD2 family HDACs play an important role in plant growth and stress response, the coordination of HD2s in these processes remains largely unknown. We found that HD2-type, HD2A and HD2C coordinate to play a role in drought stress response in Arabidopsis. We showed that the hd2a.hd2c double mutant (Mac16) exhibit decreased drought survival and increased water loss as compared to the single mutants, hd2a and hd2c. Gene expression analysis showed that the ABI1 and ABI2 genes were upregulated and SLAC1 was downregulated which led to the modified stomatal functioning in the Mac16 as compared to the single mutants. Overexpression of HD2A and HD2C showed enhanced drought survival and decreased water loss. We also showed that the GA2ox1 and GA2ox2 genes, which are involved in the catabolism of bioactive gibberellic acids, were upregulated in the Mac16 as compared to the single mutants, which led to a decreased root growth in the Mac16. Furthermore, we showed that HD2A and HD2C can physically interact and increased genome-wide H3K9 acetylation was observed in the Mac16, compared to the single mutants. Overall, our investigation revealed that HD2A and HD2C coordinate to play a cumulative role in drought stress response and root growth in Arabidopsis.

Response of Cyanic and Acyanic Lettuce Cultivars to an Increased Proportion of Blue Light

Indoor crop cultivation systems such as vertical farms or plant factories necessitate artificial lighting. Light spectral quality can affect plant growth and metabolism and, consequently, the amount of biomass produced and the value of the produce. Conflicting results on the effects of the light spectrum in different plant species and cultivars make it critical to implement a singular lighting solution. In this study we investigated the response of cyanic and acyanic lettuce cultivars to an increased proportion of blue light. For that, we selected a green and a red leaf lettuce cultivar (i.e., 'Aquino', CVg, and 'Barlach', CVr, respectively). The response of both cultivars to long-term blue-enriched light application compared to a white spectrum was analyzed. Plants were grown for 30 days in a growth chamber with optimal environmental conditions (temperature: 20 °C, relative humidity: 60%, ambient CO₂, photon flux density (PFD) of 260 µmol m^-2 s^-1 over an 18 h photoperiod). At 15 days after sowing (DAS), white spectrum LEDs (WW) were compared to blue-enriched light (WB; λ_Peak = 423 nm) maintaining the same PFD of 260 µmol m^-2 s^-1. At 30 DAS, both lettuce cultivars adapted to the blue light variant, though the adaptive response was specific to the variety. The rosette weight, light use efficiency, and maximum operating efficiency of PSII photochemistry in the light, F_v/F_m', were comparable between the two light treatments. A significant light quality effect was detected on stomatal density and conductance (20% and 17% increase under WB, respectively, in CVg) and on the modified anthocyanin reflectance index (mARI) (40% increase under WB, in CVr). Net photosynthesis response was generally stronger in CVg compared to CVr; e.g., net photosynthetic rate, P_n, at 1000 µmol m^-2 s^-1 PPFD increased from WW to WB by 23% in CVg, compared to 18% in CVr. The results obtained suggest the occurrence of distinct physiological adaptive strategies in green and red pigmented lettuce cultivars to adapt to the higher proportion of blue light environment.

Role of the mismatch repair protein MSH7 in Arabidopsis adaptation to acute salt stress

DNA mismatch repair (MMR) is a highly conserved pathway in evolution responsible for maintaining genomic stability. MMR is initiated when MutS proteins recognize and repair single base-base mismatches and small loops of unpaired nucleotides as well as certain types of DNA damage. Arabidopsis thaliana and other plants contain MutS protein homologs (MSH) found in other eukaryotic organisms and a unique MSH7 polypeptide. In this study, we first evaluated transient expression profiles of ten-days old pAtMSH7:GUS transgenic seedlings at different recovery times after an acute treatment for 48 hs with100 mM NaCl. GUS histochemical staining indicated that MSH7 expression is repressed by salt exposure but recovers progressively. Then, ten-days old mutants harboring two independent msh7 alleles were exposed for 48 hs with100 mM NaCl and different traits were measured over recovery time. Salt treated msh7 seedlings were defective in G2/M arrest. As a result, msh7 seedlings showed a reduced salt inhibitory effect as evidenced by a decreased reduction of rosette and leaf areas, stomatal density, total leaf number, silique length and seed number per silique. These findings suggest that disruption of MSH7 activity could be a promising approach for plant adaptive responses to salinity stress.

The Imaging of Guard Cells of thioglucosidase (tgg) Mutants of Arabidopsis Further Links Plant Chemical Defence Systems with Physical Defence Barriers

The glucosinolate-myrosinase system is a well-known plant chemical defence system. Two functional myrosinase-encoding genes, THIOGLUCOSIDASE 1 (TGG1) and THIOGLUCOSIDASE 2 (TGG2), express in aerial tissues of Arabidopsis. TGG1 expresses in guard cells (GCs) and is also a highly abundant protein in GCs. Recently, by studying wild type (WT), tgg single, and double mutants, we showed a novel association between the glucosinolate-myrosinase system defence system, and a physical barrier, the cuticle. In the current study, using imaging techniques, we further analysed stomata and ultrastructure of GCs of WT, tgg1, tgg2 single, and tgg1 tgg2 double mutants. The tgg mutants showed distinctive features of GCs. The GCs of tgg1 and tgg1 tgg2 mutants showed vacuoles that had less electron-dense granular material. Both tgg single mutants had bigger stomata complexes. The WT and tgg mutants also showed variations for cell wall, chloroplasts, and starch grains of GCs. Abscisic acid (ABA)-treated stomata showed that the stomatal aperture was reduced in tgg1 single and tgg1 tgg2 double mutants. The data provides a basis to perform comprehensive further studies to find physiological and molecular mechanisms associated with ultrastructure differences in tgg mutants. We speculate that the absence of myrosinase alters the endogenous chemical composition, hence affecting the physical structure of plants and the plants' physical defence barriers.

Genetic variation for tolerance to the downy mildew pathogen Peronospora variabilis in genetic resources of quinoa (Chenopodium quinoa)

BACKGROUND

Quinoa (Chenopodium quinoa Willd.) is an ancient grain crop that is tolerant to abiotic stress and has favorable nutritional properties. Downy mildew is the main disease of quinoa and is caused by infections of the biotrophic oomycete Peronospora variabilis Gaüm. Since the disease causes major yield losses, identifying sources of downy mildew tolerance in genetic resources and understanding its genetic basis are important goals in quinoa breeding.

RESULTS

We infected 132 South American genotypes, three Danish cultivars and the weedy relative C. album with a single isolate of P. variabilis under greenhouse conditions and observed a large variation in disease traits like severity of infection, which ranged from 5 to 83%. Linear mixed models revealed a significant effect of genotypes on disease traits with high heritabilities (0.72 to 0.81). Factors like altitude at site of origin or seed saponin content did not correlate with mildew tolerance, but stomatal width was weakly correlated with severity of infection. Despite the strong genotypic effects on mildew tolerance, genome-wide association mapping with 88 genotypes failed to identify significant marker-trait associations indicating a polygenic architecture of mildew tolerance.

CONCLUSIONS

The strong genetic effects on mildew tolerance allow to identify genetic resources, which are valuable sources of resistance in future quinoa breeding.