MAIN CONCLUSION: Cell expression is coordinated with chloroplast division in diploid and tetraploid Arabidopsis thaliana, polyploidy promoted the expansion of mesophyll cells and chloroplast division in A. thaliana. Cell development and differentiation are always accompanied by cell expansion and chloroplast division in plants, but the relationship between them is still relatively unknown. To confirm the relationship between cell expansion and chloroplast division during the leaf development process of diploid and tetraploid Arabidopsis thaliana, we systematically analyzed the expansion of mesophyll cells and the division of chloroplasts through cytological observation and gene-expression characteristics. As a result, in diploid and tetraploid A. thaliana, there were two peaks in both mesophyll cell expansion and chloroplast division during the leaf development process. Tetraploid A. thaliana mesophyll cells were larger and contained more chloroplasts than diploid A. thaliana mesophyll cells, which indicated that cell division and cell expansion were coordinated with chloroplast division in A. thaliana and that polyploidy further promoted mesophyll cell expansion and chloroplast division.

To deeply investigate the pivotal roles of Auxin (mainly indole-3-acetic acid, IAA), it is essential to obtain the contents of IAA in different locations of plants. It is still a challenge to quantify the levels of IAA in different sites of Arabidopsis thaliana leaves because of the small sizes. In this study, a simple paper-based electroanalytical device coupled with microsampling was used to differentiate the IAA amounts in different locations of Arabidopsis thaliana leaves. For the micro real sampling, the different areas of the thaliana leaves were retrieved by the Harris Uni-Core TM Miltex® with diameters: 1.0, 1.5, 2.5, 3.5, and 4.0 mm. The results showed that the contents of IAA can be detected from circle samples with the diameter from 1.0 to 4.0 mm. With 1.5 mm diameter sampling, the levels of IAA could be obtained in different sites of cotyledon and the first true leaf of Arabidopsis thaliana at the seedling stage. Our results suggested that the highest IAA levels were in the near petiole and lowest IAA levels in the leaf tip, which roughly agreed with those in tobacco leaves based on HPLC-MS reported before. In addition, the microsampling has a minor impact on the growth of Arabidopsis thaliana in the following especially for circle samples with the diameter 1.5 mm. This study revealed the potential application of microsampling coupled with a simple paper-based electroanalytical device for the mapping study of IAA in small plants or small tissue samples.

Here, the authors conduct a genome-wide association study from Arabidopsis thaliana accessions and demonstrate that the polymorphisms in the promoter of NRT1.1/NPF6.3, a dual-affinity nitrate transporter, are associated with different magnitudes of N deficiency in Arabidopsis shoot.

EGY1 (ethylene-dependent gravitropism-deficient and yellow-green 1) is an intramembrane metalloprotease located in chloroplasts, involved in many diverse processes including chloroplast development, chlorophyll biosynthesis, and the ethylene-dependent gravitropic response. Plants deprived of this protease display pleiotropic effects such as the yellow-green early senescence phenotype and a poorly developed thylakoid system membrane in the mature chloroplasts. We applied the GC/MS technique to analyze the changes in fatty acid composition in two egy1 mutant lines. We used DAPI staining and transmission electron microscopy methods to establish the number of nucleoids and the amount of chloroplast DNA. Our results indicated that the lack of EGY1 protease led to a dramatic overaccumulation and a dramatic decrease in the content of linolenic acid C18:3 and hexadecatrienoic acid C16:3, respectively. The amount of chloroplast DNA and the number of nucleoids were severely reduced in egy1 mutant lines. Similarly, a reduced correlation between DAPI and autofluorescence signal was observed, which may indicate some perturbations in nucleoid anchoring.

In plants, the trafficking mechanisms by which sterols move through the plant and into target cells are unknown. Earlier studies identified endosomes as primary candidates for internalization of sterols in plants, but these results have come into question. Here, we show that in elongating root cells, the internalization of sterol occurs primarily by a non-endocytic mechanism. Added fluorescent sterols [dehydroergosterol (DHE) and BODIPY-cholesterol (BCh)] do not initially label endosomes identified by fluorescent protein markers or by internalized FM4-64. Instead, the nuclear envelope, an organelle not associated with the endocytic pathway but part of the endoplasmic reticulum (ER), becomes labeled. This result is supported by experiments with the inducible overexpression of auxilin-2-like protein (AUX2 line), which blocks most endocytosis upon induction. Internalization and nuclear envelope labeling still occur in induced AUX2 cells. Longer-term incubation labels the oil body, a site involved in sterol storage. Although the first site of localization, the nuclear envelope, is part of the ER, other domains of the ER do not accumulate the label. The trafficking pathway differs from vesicular endocytosis and points toward a different pathway of sterol transport possibly involving other mechanisms, such as ER–plasma membrane contact sites and cytoplasmic transport.

Plants are not only challenged by pathogenic organisms but also colonized by commensal microbes. The network of interactions these microbes establish with their host and among each other is suggested to contribute to the immune responses of plants against pathogens. In wild Arabidopsis thaliana populations, the oomycete pathogen Albugo laibachii plays an influential role in structuring the leaf phyllosphere. We show that the epiphytic yeast Moesziomyces bullatus ex Albugo on Arabidopsis, a close relative of pathogenic smut fungi, is an antagonistic member of the A. thaliana phyllosphere, which reduces infection of A. thaliana by A. laibachii. Combination of transcriptomics, reverse genetics, and protein characterization identified a GH25 hydrolase with lysozyme activity as a major effector of this microbial antagonism. Our findings broaden the understanding of microbial interactions within the phyllosphere, provide insights into the evolution of epiphytic basidiomycete yeasts, and pave the way for novel biocontrol strategies.

Trabajo presentado al International Symposium on Plant Photobiology (ISPP), celebrado virtualmente del 22 al 25 de julio de 2021. | Peer reviewed