Analysis of a novel mutant allele of GSL8 reveals its key roles in cytokinesis and symplastic trafficking in Arabidopsis
Saatian, B., Austin, R.S., Tian, G., Chen, C., Nguyen, V., Kohalmi, S.E., Geelen, D., Cui, Y. (2018). Analysis of a novel mutant allele of GSL8 reveals its key roles in cytokinesis and symplastic trafficking in Arabidopsis. BMC Plant Biology, [online] 18(1), http://dx.doi.org/10.1186/s12870-018-1515-y
Plain language summary
Plant cell walls are rich in polysaccharides such as cellulose and callose. Callose deposition within the cell is highly regulated and occurs through interaction of different components. Even though 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 synthase, also known as Glucan Synthase-Like (GSL) is a key player in early seedling development and is required for maintaining the basic number of genes and regulating the signalling processes between cells. In this study, we used Arabidopsis thaliana as a model plant and focused on GSL8 gene. We showed that a mutation on GSL8 gene (named essp8 or gsl8) causes observable developmental defects and lethality in Arabidopsis plants. GSL8 is required for proper cell division in embryonic root. Therefore, gsl8 mutant causes dwarfism, formation of abnormally developed cotyledons and true leaves, reduced growth of roots and hypocotyl, and generally delayed development compared to wild type. The essp8 mutation also causes lethality in 20 % of the seeds and thus, reduced transmission in the progeny.
Background: Plant 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. Results: CALLOSE 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. Conclusion: Analysis 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.