The Control of Single-Celled Cotton Fiber Elongation by Developmentally Reversible Gating of Plasmodesmata and Coordinated Expression of Sucrose and K + Transporters and Expansin

Abstract

Each cotton fiber is a single cell that elongates to 2.5 to 3.0 cm from the seed coat epidermis within approximately 16 days after anthesis (DAA). To elucidate the mechanisms controlling this rapid elongation, we studied the gating of fiber plasmodesmata and the expression of the cell wall-loosening gene expansin and plasma membrane transporters for sucrose and K(+), the major osmotic solutes imported into fibers. Confocal imaging of the membrane-impermeant fluorescent solute carboxyfluorescein (CF) revealed that the fiber plasmodesmata were initially permeable to CF (0 to 9 DAA), but closed at approximately 10 DAA and re-opened at 16 DAA. A developmental switch from simple to branched plasmodesmata was also observed in fibers at 10 DAA. Coincident with the transient closure of the plasmodesmata, the sucrose and K(+) transporter genes were expressed maximally in fibers at 10 DAA with sucrose transporter proteins predominately localized at the fiber base. Consequently, fiber osmotic and turgor potentials were elevated, driving the rapid phase of elongation. The level of expansin mRNA, however, was high at the early phase of elongation (6 to 8 DAA) and decreased rapidly afterwards. The fiber turgor was similar to the underlying seed coat cells at 6 to 10 DAA and after 16 DAA. These results suggest that fiber elongation is initially achieved largely by cell wall loosening and finally terminated by increased wall rigidity and loss of higher turgor. To our knowledge, this study provides an unprecedented demonstration that the gating of plasmodesmata in a given cell is developmentally reversible and is coordinated with the expression of solute transporters and the cell wall-loosening gene. This integration of plasmodesmatal gating and gene expression appears to control fiber cell elongation.

The calcium sensor GhCaM7 promotes cotton fiber elongation by modulating reactive oxygen species (ROS) production

“…Cotton fiber elongation is initiated largely by cell wall loosening and terminated by increased wall rigidity and loss of turgor (Ruan et al, 2001). Ca 2+ and ROS are reported to play important roles in the early stages of fiber elongation, mainly on the basis of evidence from transcription analysis (Lee et al, 2007;Taliercio & Boykin, 2007;Mei et al, 2009;Zhang et al, 2010;Padmalatha et al, 2012;Walford et al, 2012).…”

Cotton fiber elongation requires the transcription factor GhMYB212 to regulate sucrose transportation into expanding fibers

“…Fibers are trichome-like structures derived from the outer epidermis cells of ovules (Basra & Malik, 1984). After initiation, fiber cells on the ovular surface elongate rapidly within 3 wk reaching up to 80% of the length of mature fibers (2.5-3.5 cm) (Ruan et al, 2001). The rate and duration of fiber cell elongation are directly associated with the length of mature fibers, and ultimately determine cotton fiber index and fiber yield, to some extent (Ruan et al, 1997).…”

“…At the late stage of fiber elongation (from 10 to 15 d post anthesis (DPA)), GhSUT1 is characterized to act as a plasma membrane H + /sucrose transporter at the base regions of fiber cells, and its protein expression reaches its maximum level after closure of the PD (Ruan et al, 2001). GhPdBG3-2A/D may participate in callose degradation at the PD, and contribute to the establishment of the symplasmic pathway (Zhang et al, 2017).…”

“…Cytological studies and transcriptional data revealed that cotton fiber cells begin fast elongation from 3 DPA and logarithmic growth lasts for 10 d (Ruan et al, 2001). Emerging investigations have indicated that, at early stage of fiber elongation, sugar transportation from ovule epidermis to developing fibers not only depends on the symplastic pathway but also needs sugar transporters such as SUTs (Ruan et al, 1997(Ruan et al, , 2001. Previous studies have revealed that phytohormone (such as auxin, brassinosteroids, gibberellin, ethylene or jasmonic acid) signalling pathways (Sun et al, 2004;Shi et al, 2006;Lee et al, 2007;Zhang et al, 2011;Tan et al, 2012), some genes (e.g.…”

Cotton Fiber Growth in Planta and in Vitro. Models for Plant Cell Elongation and Cell Wall Biogenesis

“…Fiber growth occurs by intercalation of materials throughout the fiber length and by tip growth (Seagull, 1990a). Solute movement into the fiber cell during cell expansion was shown recently to result from developmentally reversible gating of plasmodesmata (Ruan et al, 2001). Amplification of nDNA has been measured in fiber cells up to 5 DPA (van't Hof, 1999) and may occur over a longer period.…”