The mRNA of a Knotted1-like transcription factor of potato is phloem mobile

Abstract

Potato Homeobox1 (POTH1) is a Knotted1-like transcription factor from the Three Amino Acid Loop Extension (TALE) superfamily that is involved in numerous aspects of development in potato (Solanum tuberosum L). POTH1 interacts with its protein partner, StBEL5, to facilitate binding to specific target genes to modulate hormone levels, mediate leaf architecture, and enhance tuber formation. In this study, promoter analyses show that the upstream sequence of POTH1 drives β-glucuronidase activity in response to light and in association with phloem cells in both petioles and stems. Because POTH1 transcripts have previously been detected in phloem cells, long-distance movement of its mRNA was tested. Using RT-PCR and transgenic potato lines over-expressing POTH1, in vitro micrografts demonstrated unilateral movement of POTH1 RNA in a rootward direction. Movement across a graft union into leaves from newly arising axillary shoots and roots of wild type stocks was verified using soil-grown tobacco heterografts. Leaves from the wild type stock containing the mobile POTH1 RNA exhibited a reduction in leaf size relative to leaves from wild type grafts. Both untranslated regions of POTH1 when fused to an expression marker β-glucuronidase, repressed its translation in tobacco protoplasts. RNA/protein binding assays demonstrated that the UTRs of POTH1 bind to two RNA-binding proteins, a polypyrimidine tract-binding protein and an alba-domain type. Conserved glycerol-responsive elements (GRE), specific to alba-domain interaction, are duplicated in both the 5' and 3' untranslated regions of POTH1. These results suggest that POTH1 functions as a mobile signal in regulating development.

MicroRNA156: A Potential Graft-Transmissible MicroRNA That Modulates Plant Architecture and Tuberization in Solanum tuberosum ssp. andigena

“…Grafts were made with wild-type and miR156 OE transgenic potato plants as per our previous protocol (Mahajan et al, 2012). miR156 OE lines were used as scions and wild-type plants as stock (heterografts), while for reverse grafting, miR156 OE plants served as stock and wild-type plants as scion (reverse grafts).…”

“…A well-established example is the movement of FLOWERING TIME protein from leaves to the shoot apex in Arabidopsis (Arabidopsis thaliana) as a longdistance signal for the regulation of flowering time (Corbesier et al, 2007). Similarly, the movement of transcripts such as GIBBERELLIC ACID INSENSITIVE (Haywood et al, 2005), BELL1 LIKE TRANSCRIPTION FACTOR5 (Banerjee et al, 2006a;Lin et al, 2013), TOMATO KNOTTED2 (Kim et al, 2001), and POTATO HOMEOBOX1 TRANSCRIPTION FACTOR (Mahajan et al, 2012), acting as long-distance signals for plant developmental processes such as leaf development, tuberization, and root growth, has been demonstrated. The movement of small interfering RNAs is also reported in a few cases where the induction of posttranscriptional gene silencing against viruses has been well studied (Waterhouse et al, 2001).…”

PbWoxT1 mRNA from pear (Pyrus betulaefolia) undergoes long‐distance transport assisted by a polypyrimidine tract binding protein

“…The long-distance transport of such mRNAs is related to the presence of a 3 0 -UTR stem ring hairpin structure and a 5 0 end polypyrimidine CU structure (Banerjee et al, 2009;Ham et al, 2009;Huang & Yu, 2009;Mahajan et al, 2012), which have been shown to mediate interactions with specific proteins to form a ribonucleoprotein (RNP) complex in the case of some mobile mRNAs (Lucas et al, 1995;Ham et al, 2009;Li et al, 2011). Proteins within the phloem companion cells facilitate the trafficking of these mRNAs through the plasmodesmata into the sieve tube system, where long-distance transport appears to be regulated by phloem-specific RNA-binding proteins (RBPs) (Lough & Lucas, 2006).…”

Transcript Abundance Explains mRNA Mobility Data in Arabidopsis thaliana

“…Interestingly, these data suggest that a large percentage of mRNA can move against the direction of phloem flow. Phenotypic changes related to specific mobile mRNAs have been reported (Kim et al, 2001;Haywood et al, 2005;Banerjee et al, 2006;Mahajan et al, 2012;Notaguchi et al, 2012), but it remains unclear to what extent mRNA mobility is biologically meaningful (Lough and Lucas, 2006;Notaguchi, 2015). Correlation between abundance and long-distance mobility has been noted, leading to speculation that mRNA transport could occur in both a selective and nonselective manner (Kim et al, 2014;Notaguchi et al, 2015).…”