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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

Accumulation of RNA for select target genes in leaves of GAS:BEL5 plants (A) and a comparison of values in both leaves and roots (B). In these transgenic lines (■), transgenic StBEL5 transcripts are transcribed in leaves and move to roots (Lin et al., 2013). Quantitative real-time RT-PCR with gene-specific primers was used to calculate the relative amounts of each RNA. StBEL5 was included as a positive control. Each sample was measured in triplicate and normalized against StActin8 RNA. The fold change in expression was calculated as the comparative threshold cycle method value relative to the mean values obtained from the WT samples (□). The WT value is equivalent to 1.0. Standard deviations of the means of three biological replicates are shown with two and three asterisks indicating significant differences (p < 0.01 and p < 0.001, respectively) using a Student's t-test.
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Figure 5: Accumulation of RNA for select target genes in leaves of GAS:BEL5 plants (A) and a comparison of values in both leaves and roots (B). In these transgenic lines (■), transgenic StBEL5 transcripts are transcribed in leaves and move to roots (Lin et al., 2013). Quantitative real-time RT-PCR with gene-specific primers was used to calculate the relative amounts of each RNA. StBEL5 was included as a positive control. Each sample was measured in triplicate and normalized against StActin8 RNA. The fold change in expression was calculated as the comparative threshold cycle method value relative to the mean values obtained from the WT samples (□). The WT value is equivalent to 1.0. Standard deviations of the means of three biological replicates are shown with two and three asterisks indicating significant differences (p < 0.01 and p < 0.001, respectively) using a Student's t-test.

Mentions: Because the GAS:BEL5 line expresses StBEL5 in the leaves, the possibility exists that these target RNAs are up-regulated in leaves and may either move down to roots or activate pathways that lead to their induction in roots. Previous work with this system showed that several genes activated by StBEL5 in roots or stolons were not induced in leaves. These included YUCCA1a and -c, ISOPENTENYL TRANSFERASE, and StBEL5 and −22 (Lin et al., 2013, Figure 4B). One notable exception is GA2ox1 which is induced in both leaves and roots (Lin et al., 2013). As previously discussed, this increase in leaves may very likely explain the slight dwarf phenotype exhibited by GAS:BEL5 transgenic lines. An assay for leaf RNA of the four induced auxin genes, StPIN1, −2, −4, and StLAX1, in the same GAS:BEL5 line used for root induction was performed (Figure 5A). There was no induction of StLAX1 in leaves but the three PIN genes showed slight increases of their transcript levels in leaves that corresponded very closely to their induction levels in roots (Figure 5B). The one exception was StPIN2 which exhibited a 1.8-fold increase in leaves but a 4.8-fold increase in roots. This very high level of root-specific accumulation was also reported for the tomato ortholog of PIN2 (Pattison and Catala, 2012). The correlation in transcript levels in both leaves and roots for StPIN1 and −4 would suggest a similar transcriptional relationship. It is conceivable that StPIN2 transcripts are transported to roots but to date there is no report of any phloem-mobile PIN mRNAs.


Phloem-mobile messenger RNAs and root development.

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

Accumulation of RNA for select target genes in leaves of GAS:BEL5 plants (A) and a comparison of values in both leaves and roots (B). In these transgenic lines (■), transgenic StBEL5 transcripts are transcribed in leaves and move to roots (Lin et al., 2013). Quantitative real-time RT-PCR with gene-specific primers was used to calculate the relative amounts of each RNA. StBEL5 was included as a positive control. Each sample was measured in triplicate and normalized against StActin8 RNA. The fold change in expression was calculated as the comparative threshold cycle method value relative to the mean values obtained from the WT samples (□). The WT value is equivalent to 1.0. Standard deviations of the means of three biological replicates are shown with two and three asterisks indicating significant differences (p < 0.01 and p < 0.001, respectively) using a Student's t-test.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3713340&req=5

Figure 5: Accumulation of RNA for select target genes in leaves of GAS:BEL5 plants (A) and a comparison of values in both leaves and roots (B). In these transgenic lines (■), transgenic StBEL5 transcripts are transcribed in leaves and move to roots (Lin et al., 2013). Quantitative real-time RT-PCR with gene-specific primers was used to calculate the relative amounts of each RNA. StBEL5 was included as a positive control. Each sample was measured in triplicate and normalized against StActin8 RNA. The fold change in expression was calculated as the comparative threshold cycle method value relative to the mean values obtained from the WT samples (□). The WT value is equivalent to 1.0. Standard deviations of the means of three biological replicates are shown with two and three asterisks indicating significant differences (p < 0.01 and p < 0.001, respectively) using a Student's t-test.
Mentions: Because the GAS:BEL5 line expresses StBEL5 in the leaves, the possibility exists that these target RNAs are up-regulated in leaves and may either move down to roots or activate pathways that lead to their induction in roots. Previous work with this system showed that several genes activated by StBEL5 in roots or stolons were not induced in leaves. These included YUCCA1a and -c, ISOPENTENYL TRANSFERASE, and StBEL5 and −22 (Lin et al., 2013, Figure 4B). One notable exception is GA2ox1 which is induced in both leaves and roots (Lin et al., 2013). As previously discussed, this increase in leaves may very likely explain the slight dwarf phenotype exhibited by GAS:BEL5 transgenic lines. An assay for leaf RNA of the four induced auxin genes, StPIN1, −2, −4, and StLAX1, in the same GAS:BEL5 line used for root induction was performed (Figure 5A). There was no induction of StLAX1 in leaves but the three PIN genes showed slight increases of their transcript levels in leaves that corresponded very closely to their induction levels in roots (Figure 5B). The one exception was StPIN2 which exhibited a 1.8-fold increase in leaves but a 4.8-fold increase in roots. This very high level of root-specific accumulation was also reported for the tomato ortholog of PIN2 (Pattison and Catala, 2012). The correlation in transcript levels in both leaves and roots for StPIN1 and −4 would suggest a similar transcriptional relationship. It is conceivable that StPIN2 transcripts are transported to roots but to date there is no report of any phloem-mobile PIN mRNAs.

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