Abstract
BackgroundPlant cell walls are mainly composed of polysaccharides such as cellulose and callose. Callose exists at a very low level in the cell wall; however, it plays critical roles at different stages of plant development as well as in defence against unfavorable conditions. Callose is accumulated at the cell plate, at plasmodesmata and in male and female gametophytes. Despite the important roles of callose in plants, the mechanisms of its synthesis and regulatory properties are not well understood.ResultsCALLOSE SYNTHASE (CALS) genes, also known as GLUCAN SYNTHASE-LIKE (GSL), comprise a family of 12 members in Arabidopsis thaliana. Here, we describe a new allele of GSL8 (named essp8) that exhibits pleiotropic seedling defects. Reduction of callose deposition at the cell plates and plasmodesmata in essp8 leads to ectopic endomitosis and an increase in the size exclusion limit of plasmodesmata during early seedling development. Movement of two non-cell-autonomous factors, SHORT ROOT and microRNA165/6, both required for root radial patterning during embryonic root development, are dysregulated in the primary root of essp8. This observation provides evidence for a molecular mechanism explaining the gsl8 root phenotype. We demonstrated that GSL8 interacts with PLASMODESMATA-LOCALIZED PROTEIN 5, a β-1,3-glucanase, and GSL10. We propose that they all might be part of a putative callose synthase complex, allowing a concerted regulation of callose deposition at plasmodesmata.ConclusionAnalysis of a novel mutant allele of GSL8 reveals that GSL8 is a key player in early seedling development in Arabidopsis. GSL8 is required for maintaining the basic ploidy level and regulating the symplastic trafficking. Callose deposition at plasmodesmata is highly regulated and occurs through interaction of different components, likely to be incorporated into a callose biosynthesis complex. We are providing new evidence supporting an earlier hypothesis that GSL8 might have regulatory roles apart from its enzymatic function in plasmodesmata regulation.
Highlights
Plant cell walls are mainly composed of polysaccharides such as cellulose and callose
Developmental defects in essp8 seedlings are caused by a splice site mutation in GLUCAN SYNTHASE-LIKE 8 (GSL8) essp8 seedlings exhibit several developmental defects including dwarfism, formation of abnormally-developed cotyledons and true leaves, reduced growth of the root and hypocotyl, and generally delayed development compared to wild type (WT) Col-0 (Fig. 1a-c)
Our current study reports the critical role of GSL8 during early seedling development in Arabidopsis
Summary
Plant cell walls are mainly composed of polysaccharides such as cellulose and callose. Callose exists at a very low level in the cell wall; it plays critical roles at different stages of plant development as well as in defence against unfavorable conditions. Callose is accumulated at the cell plate, at plasmodesmata and in male and female gametophytes. Plant cell walls are rich in polysaccharides such as cellulose and callose [1]. Even though in plants callose is accumulated in the cell wall at a lower ratio compared to cellulose, it plays significant roles [2]. At the end of anaphase, a tubulovesicular network is formed at the equator of dividing cells [9, 10].
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