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Phloem-mobile messenger RNAs and root development.

Hannapel DJ, Sharma P, Lin T - Front Plant Sci (2013)

Bottom Line: In another example, heterografting techniques were used to identify phloem-mobile Aux/IAA transcripts in Arabidopsis.Phloem transport of both StBEL5 and Aux/IAA RNAs are linked to hormone metabolism and both target auxin synthesis genes or auxin signaling processes.The mechanisms of transport for these mobile RNAs, the impact they have on controlling root growth, and a potential transcriptional connection between the BEL1/KNOX complex and Aux/IAA genes are discussed.

View Article: PubMed Central - PubMed

Affiliation: Plant Biology Major, Iowa State University Ames, IA, USA.

ABSTRACT
Numerous signal molecules move through the phloem to regulate development, including proteins, secondary metabolites, small RNAs and full-length transcripts. Several full-length mRNAs have been identified that move long distances in a shootward or rootward direction through the plant vasculature to modulate both floral and vegetative processes of growth. Here we discuss two recently discovered examples of long-distance transport of full-length mRNAs into roots and the potential target genes and pathways for these mobile signals. In both cases, the mobile RNAs regulate root growth. Previously, RNA movement assays demonstrated that transcripts of StBEL5, a transcription factor from the three-amino-loop-extension superclass, move through the phloem to stolon tips to enhance tuber formation in potato (Solanum tuberosum L.). StBEL5 mRNA originates in the leaf and its movement to stolons is induced by a short-day photoperiod. Movement of StBEL5 RNA to roots correlated with increased growth and the accumulation of several transcripts associated with hormone metabolism, including GA2-oxidase1, YUCCA1a and -c, several Aux/IAA types, and PIN1, -2, and -4 was observed. In another example, heterografting techniques were used to identify phloem-mobile Aux/IAA transcripts in Arabidopsis. Movement assays confirmed that these Aux/IAA transcripts are transported into the root system where they suppress lateral root formation. Phloem transport of both StBEL5 and Aux/IAA RNAs are linked to hormone metabolism and both target auxin synthesis genes or auxin signaling processes. The mechanisms of transport for these mobile RNAs, the impact they have on controlling root growth, and a potential transcriptional connection between the BEL1/KNOX complex and Aux/IAA genes are discussed.

No MeSH data available.


Related in: MedlinePlus

Movement of transgenic StBEL5 mRNA from leaf to root. Quantification of movement was performed on transgenic lines expressing full-length StBEL5 RNA driven by the galactinol synthase (GAS) promoter of melon (Cucumis melo) (A). This promoter is predominately expressed in the minor veins of leaf mesophyll but not in other parts of the plant (Ayre et al., 2003; Banerjee et al., 2009). Relative levels of StBEL5 RNA were quantified (A) from total RNA extracted from new leaves (■), and from either primary (□) or secondary () root samples of a SD-grown GAS:BEL5 transgenic plants. One-step RT-PCR was performed using 200–250 ng of total RNA, a primer for the NOS terminator sequence specific to all transgenic RNAs and a gene-specific primer for the full-length StBEL5 transcript. These primers specifically amplify only transgenic BEL5 RNA. All PCR reactions were standardized and optimized to yield product in the linear range. Homogenous PCR products were quantified by using ImageJ software (Abramoff et al., 2004) and normalized by using 18S rRNA values. Standard errors of the means of three replicate samples are shown. For heterografts (B), micrografts were performed with replicates of either GAS:BEL5 scions on WT andigena stocks or GAS:GUS scions on WT andigena stocks. After 2 weeks in culture, grafts were moved to soil and grown under LDs for 3 weeks and then under SDs for 2 weeks before harvest of roots and leaves. After RNA extraction, RT-PCR with gene-specific primers was performed on RNA from WT lateral roots of both heterografts. A second PCR was performed with nested primers for both types. RNA from scion leaf samples was used as a positive control (scion samples). Two different gene-specific primers were used with a non-plant sequence tag specific for the transgenic StBEL5 RNA to discriminate from the native RNA. Four plants were assayed for both heterografts and are designated 1–4. Wild-type RNA from lateral roots of whole plants (S. tuberosum ssp. andigena) was used in the RT-PCR reactions with StBEL5 transgenic GSPs as a negative control (WT root). Similar negative results were obtained with RNA from WT leaves. (reprinted from Figure 1 of Lin et al., 2013; Copyright American Society of Plant Biologists, www.plantphysiol.org).
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Figure 1: Movement of transgenic StBEL5 mRNA from leaf to root. Quantification of movement was performed on transgenic lines expressing full-length StBEL5 RNA driven by the galactinol synthase (GAS) promoter of melon (Cucumis melo) (A). This promoter is predominately expressed in the minor veins of leaf mesophyll but not in other parts of the plant (Ayre et al., 2003; Banerjee et al., 2009). Relative levels of StBEL5 RNA were quantified (A) from total RNA extracted from new leaves (■), and from either primary (□) or secondary () root samples of a SD-grown GAS:BEL5 transgenic plants. One-step RT-PCR was performed using 200–250 ng of total RNA, a primer for the NOS terminator sequence specific to all transgenic RNAs and a gene-specific primer for the full-length StBEL5 transcript. These primers specifically amplify only transgenic BEL5 RNA. All PCR reactions were standardized and optimized to yield product in the linear range. Homogenous PCR products were quantified by using ImageJ software (Abramoff et al., 2004) and normalized by using 18S rRNA values. Standard errors of the means of three replicate samples are shown. For heterografts (B), micrografts were performed with replicates of either GAS:BEL5 scions on WT andigena stocks or GAS:GUS scions on WT andigena stocks. After 2 weeks in culture, grafts were moved to soil and grown under LDs for 3 weeks and then under SDs for 2 weeks before harvest of roots and leaves. After RNA extraction, RT-PCR with gene-specific primers was performed on RNA from WT lateral roots of both heterografts. A second PCR was performed with nested primers for both types. RNA from scion leaf samples was used as a positive control (scion samples). Two different gene-specific primers were used with a non-plant sequence tag specific for the transgenic StBEL5 RNA to discriminate from the native RNA. Four plants were assayed for both heterografts and are designated 1–4. Wild-type RNA from lateral roots of whole plants (S. tuberosum ssp. andigena) was used in the RT-PCR reactions with StBEL5 transgenic GSPs as a negative control (WT root). Similar negative results were obtained with RNA from WT leaves. (reprinted from Figure 1 of Lin et al., 2013; Copyright American Society of Plant Biologists, www.plantphysiol.org).

Mentions: Using both movement assays in whole plants (Figure 1A) and heterografts of GAS:BEL5 scions and WT stocks (Figure 1B), movement of transgenic StBEL5 into roots was tested. The GAS promoter drives leaf-specific expression (Ayre et al., 2003) and in whole transgenic GAS:BEL5 plants, substantial amounts of transgenic StBEL5 RNA were transported into both primary and lateral roots (Figure 1A). To confirm this movement, heterografts of GAS:BEL5 scions and WT stocks were performed and RT-PCR assays were used to detect the StBEL5 transgenic RNA in the roots of WT stock material (Figure 1B). As a negative control GAS:GUS transgenic lines were grafted as scions onto WT stocks. Transgenic StBEL5 RNA was detected in lateral roots of WT stock from four separate GAS:BEL5/WT heterografts whereas, no GUS RNA was detected in lateral roots from WT stock from four separate GAS:GUS/WT heterografts (Figure 1B). In correlation with the long-distance transport of transgenic StBEL5 into roots, root growth was enhanced in the transgenic GAS:BEL5 lines in both soil-grown and in vitro plants by approximately 75% (Figure 2A). Root growth from these transgenic lines was more vigorous and robust than in WT lines (Figure 2B).


Phloem-mobile messenger RNAs and root development.

Hannapel DJ, Sharma P, Lin T - Front Plant Sci (2013)

Movement of transgenic StBEL5 mRNA from leaf to root. Quantification of movement was performed on transgenic lines expressing full-length StBEL5 RNA driven by the galactinol synthase (GAS) promoter of melon (Cucumis melo) (A). This promoter is predominately expressed in the minor veins of leaf mesophyll but not in other parts of the plant (Ayre et al., 2003; Banerjee et al., 2009). Relative levels of StBEL5 RNA were quantified (A) from total RNA extracted from new leaves (■), and from either primary (□) or secondary () root samples of a SD-grown GAS:BEL5 transgenic plants. One-step RT-PCR was performed using 200–250 ng of total RNA, a primer for the NOS terminator sequence specific to all transgenic RNAs and a gene-specific primer for the full-length StBEL5 transcript. These primers specifically amplify only transgenic BEL5 RNA. All PCR reactions were standardized and optimized to yield product in the linear range. Homogenous PCR products were quantified by using ImageJ software (Abramoff et al., 2004) and normalized by using 18S rRNA values. Standard errors of the means of three replicate samples are shown. For heterografts (B), micrografts were performed with replicates of either GAS:BEL5 scions on WT andigena stocks or GAS:GUS scions on WT andigena stocks. After 2 weeks in culture, grafts were moved to soil and grown under LDs for 3 weeks and then under SDs for 2 weeks before harvest of roots and leaves. After RNA extraction, RT-PCR with gene-specific primers was performed on RNA from WT lateral roots of both heterografts. A second PCR was performed with nested primers for both types. RNA from scion leaf samples was used as a positive control (scion samples). Two different gene-specific primers were used with a non-plant sequence tag specific for the transgenic StBEL5 RNA to discriminate from the native RNA. Four plants were assayed for both heterografts and are designated 1–4. Wild-type RNA from lateral roots of whole plants (S. tuberosum ssp. andigena) was used in the RT-PCR reactions with StBEL5 transgenic GSPs as a negative control (WT root). Similar negative results were obtained with RNA from WT leaves. (reprinted from Figure 1 of Lin et al., 2013; Copyright American Society of Plant Biologists, www.plantphysiol.org).
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Related In: Results  -  Collection

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Figure 1: Movement of transgenic StBEL5 mRNA from leaf to root. Quantification of movement was performed on transgenic lines expressing full-length StBEL5 RNA driven by the galactinol synthase (GAS) promoter of melon (Cucumis melo) (A). This promoter is predominately expressed in the minor veins of leaf mesophyll but not in other parts of the plant (Ayre et al., 2003; Banerjee et al., 2009). Relative levels of StBEL5 RNA were quantified (A) from total RNA extracted from new leaves (■), and from either primary (□) or secondary () root samples of a SD-grown GAS:BEL5 transgenic plants. One-step RT-PCR was performed using 200–250 ng of total RNA, a primer for the NOS terminator sequence specific to all transgenic RNAs and a gene-specific primer for the full-length StBEL5 transcript. These primers specifically amplify only transgenic BEL5 RNA. All PCR reactions were standardized and optimized to yield product in the linear range. Homogenous PCR products were quantified by using ImageJ software (Abramoff et al., 2004) and normalized by using 18S rRNA values. Standard errors of the means of three replicate samples are shown. For heterografts (B), micrografts were performed with replicates of either GAS:BEL5 scions on WT andigena stocks or GAS:GUS scions on WT andigena stocks. After 2 weeks in culture, grafts were moved to soil and grown under LDs for 3 weeks and then under SDs for 2 weeks before harvest of roots and leaves. After RNA extraction, RT-PCR with gene-specific primers was performed on RNA from WT lateral roots of both heterografts. A second PCR was performed with nested primers for both types. RNA from scion leaf samples was used as a positive control (scion samples). Two different gene-specific primers were used with a non-plant sequence tag specific for the transgenic StBEL5 RNA to discriminate from the native RNA. Four plants were assayed for both heterografts and are designated 1–4. Wild-type RNA from lateral roots of whole plants (S. tuberosum ssp. andigena) was used in the RT-PCR reactions with StBEL5 transgenic GSPs as a negative control (WT root). Similar negative results were obtained with RNA from WT leaves. (reprinted from Figure 1 of Lin et al., 2013; Copyright American Society of Plant Biologists, www.plantphysiol.org).
Mentions: Using both movement assays in whole plants (Figure 1A) and heterografts of GAS:BEL5 scions and WT stocks (Figure 1B), movement of transgenic StBEL5 into roots was tested. The GAS promoter drives leaf-specific expression (Ayre et al., 2003) and in whole transgenic GAS:BEL5 plants, substantial amounts of transgenic StBEL5 RNA were transported into both primary and lateral roots (Figure 1A). To confirm this movement, heterografts of GAS:BEL5 scions and WT stocks were performed and RT-PCR assays were used to detect the StBEL5 transgenic RNA in the roots of WT stock material (Figure 1B). As a negative control GAS:GUS transgenic lines were grafted as scions onto WT stocks. Transgenic StBEL5 RNA was detected in lateral roots of WT stock from four separate GAS:BEL5/WT heterografts whereas, no GUS RNA was detected in lateral roots from WT stock from four separate GAS:GUS/WT heterografts (Figure 1B). In correlation with the long-distance transport of transgenic StBEL5 into roots, root growth was enhanced in the transgenic GAS:BEL5 lines in both soil-grown and in vitro plants by approximately 75% (Figure 2A). Root growth from these transgenic lines was more vigorous and robust than in WT lines (Figure 2B).

Bottom Line: In another example, heterografting techniques were used to identify phloem-mobile Aux/IAA transcripts in Arabidopsis.Phloem transport of both StBEL5 and Aux/IAA RNAs are linked to hormone metabolism and both target auxin synthesis genes or auxin signaling processes.The mechanisms of transport for these mobile RNAs, the impact they have on controlling root growth, and a potential transcriptional connection between the BEL1/KNOX complex and Aux/IAA genes are discussed.

View Article: PubMed Central - PubMed

Affiliation: Plant Biology Major, Iowa State University Ames, IA, USA.

ABSTRACT
Numerous signal molecules move through the phloem to regulate development, including proteins, secondary metabolites, small RNAs and full-length transcripts. Several full-length mRNAs have been identified that move long distances in a shootward or rootward direction through the plant vasculature to modulate both floral and vegetative processes of growth. Here we discuss two recently discovered examples of long-distance transport of full-length mRNAs into roots and the potential target genes and pathways for these mobile signals. In both cases, the mobile RNAs regulate root growth. Previously, RNA movement assays demonstrated that transcripts of StBEL5, a transcription factor from the three-amino-loop-extension superclass, move through the phloem to stolon tips to enhance tuber formation in potato (Solanum tuberosum L.). StBEL5 mRNA originates in the leaf and its movement to stolons is induced by a short-day photoperiod. Movement of StBEL5 RNA to roots correlated with increased growth and the accumulation of several transcripts associated with hormone metabolism, including GA2-oxidase1, YUCCA1a and -c, several Aux/IAA types, and PIN1, -2, and -4 was observed. In another example, heterografting techniques were used to identify phloem-mobile Aux/IAA transcripts in Arabidopsis. Movement assays confirmed that these Aux/IAA transcripts are transported into the root system where they suppress lateral root formation. Phloem transport of both StBEL5 and Aux/IAA RNAs are linked to hormone metabolism and both target auxin synthesis genes or auxin signaling processes. The mechanisms of transport for these mobile RNAs, the impact they have on controlling root growth, and a potential transcriptional connection between the BEL1/KNOX complex and Aux/IAA genes are discussed.

No MeSH data available.


Related in: MedlinePlus