Abstract
Root hair cells form the primary interface of plants with the soil environment, playing key roles in nutrient uptake and plant defense. In legumes, they are typically the first cells to become infected by nitrogen-fixing soil bacteria during root nodule symbiosis. Here, we report a role for the CELLULOSE SYNTHASE-LIKE D1 (CSLD1) gene in root hair development in the legume species Lotus japonicus. CSLD1 belongs to the cellulose synthase protein family that includes cellulose synthases and cellulose synthase-like proteins, the latter thought to be involved in the biosynthesis of hemicellulose. We describe 11 Ljcsld1 mutant alleles that impose either short (Ljcsld1-1) or variable (Ljcsld1-2 to 11) root hair length phenotypes. Examination of Ljcsld1-1 and one variable-length root hair mutant, Ljcsld1-6, revealed increased root hair cell wall thickness, which in Ljcsld1-1 was significantly more pronounced and also associated with a strong defect in root nodule symbiosis. Lotus japonicus plants heterozygous for Ljcsld1-1 exhibited intermediate root hair lengths, suggesting incomplete dominance. Intragenic complementation was observed between alleles with mutations in different CSLD1 domains, suggesting CSLD1 function is modular and that the protein may operate as a homodimer or multimer during root hair development.
Highlights
Plant cell walls constitute a dynamic yet rigid interface between cells or between the cell and the external environment
A survey of genes present on these clones identified, among others, a Cellulose SynthaseLike D gene (LjCSLD1) located on TM0757 (Supplemental Figure S1). This gene was considered as a viable candidate for either the LjVRH1 or the LjSRH1 locus, as proteins belonging to the Arabidopsis AtCSLD subfamily, such as KOJAK, were shown to be required for root hair cell morphogenesis (Favery et al, 2001)
The same locus was amplified and sequenced from the 15 additional L. japonicus mutant lines with the Ljvrh-like phenotypes. Seven of these carried single-nucleotide substitutions within the predicted coding region of the LjCSLD1 gene (Supplemental Table S1), while the remaining lines had the wild-type LjCSLD1 sequence, suggesting that their mutant root hair phenotypes were determined by mutations in an independent locus or loci
Summary
Plant cell walls constitute a dynamic yet rigid interface between cells or between the cell and the external environment. Hemicellulose, and pectin (Lampugnani et al, 2018), cell walls vary considerably based on plant species as well as tissue type (Popper et al, 2014; Hofte and Voxeur, 2017; Penning et al, 2019). They share an important feature in their propensity for rapid remodeling both during isotropic and anisotropic expansions; this remodeling is a key to growth and survival of cells and organisms, including their ability to respond to various abiotic and biotic cues. The main structural component of plant cell walls, is synthesized by large, plasma membrane-localized complexes consisting of cellulose synthase (CESA) subunits. CESA1-, CESA3-, and CESA6-related proteins (CESA2/ 5/6/9) mediate cellulose biosynthesis in the primary cell wall, while CESA4, CESA7, and CESA8 are involved in secondary cell wall formation (Arioli et al, 1998; Taylor et al, 2003; Desprez et al, 2007; Persson et al, 2007; Lampugnani et al, 2019)
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