Biology subjects

Sarazin, A.

Publications and source records attributed to Sarazin, A..

3 recordsLinked to original sources

bioRxiv2021

A molecular framework for proximal secondary vein branching in the Arabidopsis thaliana embryo

O_LIThe establishment of a closed vascular network in foliar organs is achieved through the coordinated specification of newly recruited procambial cells, their proliferation and elongation. An important, yet poorly understood component of this process, is secondary vein branching; a mechanism employed in Arabidopsis thaliana cotyledons to extend vascular tissues throughout the organs surface by secondary vein formation. C_LIO_LITo investigate the underlying molecular mechanism in vein branching, we analyzed at a single-cell level the discontinuous vein network of cotyledon vascular pattern 2 (cvp2) cvp2-like 1 (cvl1). Utilizing live-cell imaging and genetic approaches we uncovered two distinct branching mechanisms during embryogenesis. C_LIO_LISimilar to wild type, distal veins in cvp2 cvl1 embryos emerged from the bifurcation of cell files contained in the midvein. However, the branching events giving rise to proximal veins are absent in this mutant. Restoration of proximal branching in cvp2 cvl1 cotyledons could be achieved by increasing OCTOPUS dosage as well as by silencing of RECEPTOR LIKE PROTEIN KINASE 2 (RPK2) expression. The RPK2-mediated restriction of proximal branching is auxin and CLE-independent. C_LIO_LIOur work defines a genetic network conferring plasticity to Arabidopsis embryos to adapt the spatial configuration of vascular tissues to organ growth. C_LI

plant biology↗

bioRxiv2021

In planta dynamics, transport-biases and endogenous functions of mobile siRNAs in Arabidopsis

O_LIIn RNA interference (RNAi), small-interfering (si)RNAs processed from double-stranded RNA guide ARGONAUTE(AGO) proteins to silence sequence-complementary RNA/DNA. Plant RNAi can propagate locally and systemically, but despite recent mechanistic advances, basic questions/hurdles remain unaddressed. For instance, RNAi is inferred to diffuse through plasmodesmata, yet how its dynamics in planta compares with that of established symplastic-diffusion markers remains unknown. Also unknown is why select siRNA species, or size-classes thereof, are recovered in RNAi-recipient tissues, yet only under some experimental settings. Finally, RNAi shootward movement in micro-grafted Arabidopsis - necessary to study its presumptive transgenerational effects- has not been achieved thus far and endogenous functions of mobile RNAi remain scarcely documented. C_LIO_LIFocusing on non-amplified RNAi in Arabidopsis, we show here that (i) transgenic RNAi-movement, although symplasmic, only partially recapitulates the diffusion pattern of free GFP in planta, (ii) the presence/absence of specific AGOs in incipient/traversed/recipient tissues likely explains the apparent siRNA-selectivity observed during vascular movement, (iii) stress application allows endo-siRNA translocation against the shoot-to-root phloem flow, and (iv) mobile endo-siRNAs generated from a single inverted-repeat(IR) locus, have the potential to regulate hundreds of transcripts. C_LIO_LIOur results close important knowledge-gaps, rationalize previously-noted inconsistencies between mobile RNAi settings, and provide a framework for functional endo-siRNA studies. C_LI

plant biology↗

bioRxiv2020

Polyploidy-associated paramutation in Arabidopsis is determined by small RNAs, temperature, and structure

Paramutation is a form of non-Mendelian inheritance in which the expression of a paramutable allele changes when it encounters a paramutagenic allele. This change in expression of the paramutable alleles is stably inherited even after segregation of both alleles. While the discovery of paramutation and studies of its underlying mechanism were made with alleles that change plant pigmentation, paramutation-like phenomena are known to modulate the expression of other traits and in other eukaryotes, and many cases have probably gone undetected. It is likely that epigenetic mechanisms are responsible for the phenomenon, as paramutation forms epialleles, genes with identical sequences but different expression states. This could account for the intergenerational inheritance of the paramutated allele, providing profound evidence that triggered epigenetic changes can be maintained over generations. Here, we use a case of paramutation that affects a transgenic selection reporter gene in tetraploid Arabidopsis thaliana. Our data suggest that different types of small RNA are derived from paramutable and paramutagenic epialleles. In addition, deletion of a repeat within the epiallele changes its paramutability. Further, the temperature during the growth of the epiallelic hybrids determines the degree and timing of the allelic interaction. The data further make it plausible why paramutation in this system becomes evident only in the segregating F2 population of tetraploid plants containing both epialleles. In summary, the results support a model for polyploidy-associated paramutation, with similarities as well as distinctions from other cases of paramutation. AUTHOR SUMMARYIn 1866, Gregor Mendel formulated the general principles of inheritance based on crossing experiments with pea plants. Curiously, in 1915, the progeny from crossing pea plants with a regular and a "rogue" leaf phenotype was lacking the expected segregation and recovery of the regular phenotype. This discovery was one of the first observations of non-Mendelian genetics and later demonstrated for more traits in other plants and termed paramutation. Paramutation is due to the epigenetic switch of an active gene to a silenced version which is then maintained in the inactive state in later generations. This demonstrates that acquired epigenetic changes can become permanent. Despite its early observation and numerous studies, mainly in maize and tomato, it is barely understood how paramutation is established and which parameters influence the process. We investigated a case of paramutation in Arabidopsis thaliana, crossing plants with genetically identical but epigenetically different alleles that result in resistance or sensitivity to an antibiotic in the growth medium. Paramutation did not become manifest immediately but only in the progeny of the hybrids, and only in plants with a doubled chromosome set. These features make this paramutation distinct from other cases. Our studies revealed several parameters that influence paramutation: an important role for sRNAs to initiate silencing, the sequence of the allele itself, the environmental conditions during growth of the hybrids, the developmental stage, and the copy number ratio between the alleles.

genetics↗