Callose Biosynthesis Regulates Symplastic Trafficking during Root Development

Abstract

Plant cells are connected through plasmodesmata (PD), membrane-lined channels that allow symplastic movement of molecules between cells. However, little is known about the role of PD-mediated signaling during plant morphogenesis. Here, we describe an Arabidopsis gene, CALS3/GSL12. Gain-of-function mutations in CALS3 result in increased accumulation of callose (β-1,3-glucan) at the PD, a decrease in PD aperture, defects in root development, and reduced intercellular trafficking. Enhancement of CALS3 expression during phloem development suppressed loss-of-function mutations in the phloem abundant callose synthase, CALS7 indicating that CALS3 is a bona fide callose synthase. CALS3 alleles allowed us to spatially and temporally control the PD aperture between plant tissues. Using this tool, we are able to show that movement of the transcription factor SHORT-ROOT and microRNA165 between the stele and the endodermis is PD dependent. Taken together, we conclude that regulated callose biosynthesis at PD is essential for cell signaling.

Arabidopsis BIRD Zinc Finger Proteins Jointly Stabilize Tissue Boundaries by Confining the Cell Fate Regulator SHORT-ROOT and Contributing to Fate Specification

“…n represents the number of roots counted; numbers are average and SD. BIRDs Control Tissue Boundariesin the procambial region of the vascular tissue (Bonke et al, 2003;Vatén et al, 2011), where SHR is both nuclear and cytoplasmic ( Figures 3A and 3A'). Expression of SCR in the vasculature directed nuclear SHR retention, consistent with a previous report (Koizumi et al, 2012;Figures 3B and 3B').…”

“…The HEAT domain protein SHR INTERACTING EMBRYONIC LETHAL was suggested to facilitate SHR movement through an endosome-and microtubule-dependent process (Koizumi et al, 2011;Wu and Gallagher, 2013). In addition, callose accumulation at plasmodesmata, symplastic channels that allow passage of hormones, proteins, and RNAs (Du et al, 2007;Schlereth et al, 2010;Matsuzaki et al, 2010), results in plasmodesmata closure and reduces SHR intercellular trafficking (Vatén et al, 2011). Furthermore, nuclear targeting of SHR by fusing a nuclear localization signal or by expressing SCR in the vasculature blocks SHR movement (Gallagher et al, 2004;Koizumi et al, 2012), suggesting that nuclear retention determines the range of SHR movement.…”

Selective Targeting of Mobile mRNAs to Plasmodesmata for Cell-to-Cell Movement

“…In plants, PD are the channels mediating cell-to-cell trafficking of many macromolecules 232 including proteins and microRNA (miRNA) (Vatén et al, 2011). To verify that the 233 punctate foci of FT SL24 mRNA were PD, we examined co-localization of FT SL24 mRNA 234 and PD markers.…”

“…To verify that the 233 punctate foci of FT SL24 mRNA were PD, we examined co-localization of FT SL24 mRNA 234 and PD markers. Aniline blue fluorophore (ABF) is a widely used PD marker that stains 235 callose located at the PD neck (Vatén et al, 2011). In ABF-stained N. benthamiana leaves 236 expressing MS2 FD -GFP and FT SL24 or RFP SL24 mRNA, FT SL24 signals co-localized with 237 co-localization analyses with FM4-64-stained plasma membrane showed FT SL24 mRNA 243 distributed as puncta on the plasma membrane (Supplemental Fig.…”

CHOLINE TRANSPORTER-LIKE1 is required for sieve plate development to mediate long-distance cell-to-cell communication

“…In cals7 mutants reduced callose deposition at the sieve plate leads to a reduced number of open pores per sieve plate, smaller diameter sieve pores and impaired phloem transport 22,23 . But also over accumulation of callose, as shown by the phloem-specific expression of a gain of function mutant of CalS3, inhibits phloem conductivity 24 , suggesting that callose deposition at the sieve plate has to be tightly regulated. The only gene identified so far which is specifically required to establish phloem identity is altered phloem development (APL), a MYB coiled-coil-type transcription factor 25 .…”