Rice OsCASP1 orchestrates Casparian strip formation and suberin deposition in small lateral roots to maintain nutrient homeostasis

Abstract

Arabidopsis Casparian strip membrane domain proteins (CASPs) form a transmembrane scaffold to recruit lignin biosynthetic enzymes for Casparian strip (CS) formation. Rice is a semi-aquatic plant with a more complex root structure than Arabidopsis to adapt its growing conditions, where the different deposition of lignin and suberin is crucial for adaptive responses. Here, we observed the structure of rice primary and small lateral roots (SLRs), particularly the deposition patterns of lignin and suberin in wild type and Oscasp1 mutants. We found that the appearance time and structure of CS in the roots of rice are different from those of Arabidopsis and observed suberin deposition in the sclerenchyma in wild type roots. Rice CASP1 is highly similar to AtCASPs, but its expression is concentrated in SLR tips and can be induced by salt stress especially in the steles. The loss of OsCASP1 function alters the expression of the genes involved in suberin biosynthesis and the deposition of suberin in the endodermis and sclerenchyma and leads to delayed CS formation and uneven lignin deposition in SLRs. These different depositions may alter nutrient uptake, resulting in ion imbalance in plant, withered leaves, fewer tillers, and reduced tolerance to salt stress. Our findings suggest that OsCASP1 could play an important role in nutrient homeostasis and adaptation to the growth environment.

Apoplastic barrier establishment in roots and nodules of Lotus japonicus is essential for root-shoot signaling and N-fixation

“…Our work illustrate that these species share a conserved machinery in CS formation and that this is required for the establishment and maintenance of a mutualistic inter-species relationship. This finding agrees with several studies showing that genes controlling CS establishment in Arabidopsis are conserved in rice (MYB36, CASP1, CIF1/2, SGN3), maize (ESB-like) and Brassica rapa (SGN3)(12)(13)(14)(15)(16)(17). Intriguingly, this additionally proposes that, in Lotus, the SGN pathway is MYB36-dependent.…”

“…myb36 knockouts), increased diffusion of CIF peptides results in a hyperactive SGN response, which onsets ectopic endodermal suberization and lignification (5,7). Evidence is emerging that orthologous genes involved in CS formation play a similar role in other plants (12)(13)(14)(15)(16)(17). We recently identified the Arabidopsis SGN pathway to play a crucial role in integrating the soil nitrogen (N) status into shoot responses (18).…”

Imaging plant cell walls using fluorescent stains: The beauty is in the details

“…It was extensively used to study the integrity of root Casparian strip barrier in the roots of A. thaliana and rice, 19,43 to assess the integrity of root exodermal lignin barrier in tomato (Solanum lycopersicum), 44 as well as periderm formation in Arabidopsis roots. 45 Moreover, PI is also an effective tool to assess the vitality of plant cells.…”

“…89 Together with aniline blue, it was used to stain poplar roots, 90 zonal geranium (Pelargonium hortorum) roots, stems 91 as well as rice roots. 19 Noteworthy, acriflavine is a fluorescent dye that has been used to discriminate between lignified and nonlignified tissues. The fluorescence from this stain can be detected at the 530 nm emission wavelength for lignified tissue and at 600 nm for non-lignified tissue.…”

“…In addition to labelling of β‐glucans, CW is often used as a tool for outlining the cells in combination with other fluorescent stains or fluorescent proteins 14 . CW stain has been used on a wide range of plant species and diverse tissues, such as maize ( Zea mays ) root and coleoptyle 16 ; rice ( Oryza sativa ) root 19 ; soybean root and hypocotyl 14 ; Arabidopsis thaliana root, stem, leaf, 14 seed, embryo, 15 ovule 20 and gynoecium 21 ; Marchantia polymorpha gemma cup 22 ; tobacco leaf 23 ; and pea root nodules 10 . CW can be visualized with a 405 nm laser with a 425–465 nm peak emission spectrum, making it compatible for the simultaneous visualization with a set of other cell wall fluorescent dyes with longer excitation and emission wavelength, such as Basic Fuchsin (BF), Auramine O, Safranin O, Nile Red, as well as fluorescent proteins (GFP, YFP, RFP, mVenus and mCherry) as demonstrated in Arabidopsis roots of different ages, stem sections 14,24 and sugar beet roots (Figure 1B–E).…”