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The Arabidopsis LRR-RLK, PXC1, is a regulator of secondary wall formation correlated with the TDIF-PXY/TDR-WOX4 signaling pathway.

Wang J, Kucukoglu M, Zhang L, Chen P, Decker D, Nilsson O, Jones B, Sandberg G, Zheng B - BMC Plant Biol. (2013)

Bottom Line: Expression profiling using qPCR and promoter:reporter lines indicated that all three PXC genes are associated with the vasculature.Shifting pxc1 mutants from long-days to short-days showed that loss of the gene led to a dramatic reduction in secondary wall formation in xylem fibers.Transcript analysis of mutants for a variety of secondary cell wall-associated genes, including PXY/TDR indicated that the pathways mediated by PXC1 connect with those mediated by the TDIF-PXY/TDR-WOX4 system.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Environmental Science and Engineering, Tianjin University, 300072 Tianjin, China.

ABSTRACT

Background: Although a number of leucine-rich repeat receptor-like kinase-encoding genes (LRR-RLKs) have been identified in plants, a functional role has been determined for only a few. Recent studies have demonstrated that an LRR-RLK, PXY/TDR, is important for the process of secondary vascular development. Other studies have indicated that PXY/TDR is unlikely to be the sole LRR-RLK involved in this complex process.

Results: In this study, in silico analyses led to the identification of three Arabidopsis LRR-RLK genes (PXY-correlated; PXC1, 2, 3) with transcript accumulation profiles that correlated strongly with several key regulators of vascular development, including PXY/TDR, HB-8, REV, and CLE41. Expression profiling using qPCR and promoter:reporter lines indicated that all three PXC genes are associated with the vasculature. One in particular, PXC1 (At2g36570), had a strong correlation with PXY/TDR. Shifting pxc1 mutants from long-days to short-days showed that loss of the gene led to a dramatic reduction in secondary wall formation in xylem fibers. Transcript analysis of mutants for a variety of secondary cell wall-associated genes, including PXY/TDR indicated that the pathways mediated by PXC1 connect with those mediated by the TDIF-PXY/TDR-WOX4 system.

Conclusions: The data indicate that the LRR-RLK, PXC1 is involved in secondary cell wall formation in xylem fibers. Whereas further study is needed to identify the ligands and mode of action of the PXC1 protein, it is clear from this work that similarly to the shoot apical meristem (SAM), secondary vascular development requires contributions from a number of LRR-RLKs.

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A heat-map (log transformed) of qRT-PCR gene expression data for main regulators of vascular development in 5-week old wild-type Arabidopsis. Stem1 denoted the base of main inflorescence stem 10 cm in height above the uppermost rosette leaf and stem2 denoted the base of main inflorescence stem 30 cm in height above the uppermost rosette leaf. Phloem and xylem were ontained by peeling method.
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Figure 4: A heat-map (log transformed) of qRT-PCR gene expression data for main regulators of vascular development in 5-week old wild-type Arabidopsis. Stem1 denoted the base of main inflorescence stem 10 cm in height above the uppermost rosette leaf and stem2 denoted the base of main inflorescence stem 30 cm in height above the uppermost rosette leaf. Phloem and xylem were ontained by peeling method.

Mentions: Because the strongest predicted links were between PXC1 and PXY/TDR, we concentrated our efforts on this gene. To further investigate the function of PXC1 in vascular development, transcript levels of PXC1 were determined in parallel with seven known regulators of vascular development in different plant tissues including the leaf lamina (as a control), petiole, young inflorescence stem, old inflorescence stem and hypocotyl. Our data showed that the transcripts for PXY were most abundant in the xylem fraction of hypocotyls, with levels increasing in older inflorescence stems (Additional file 4C). Expression patterns for HB8, HB15 (HOMEOBOX GENE 15) and NST3 (NAC TRANSCRIPTION FACTOR3) were similar to those observed for PXY (Additional file 4A, B and D). HB8 and HB15 are both recognized as molecular markers of procambial cells [32,33] and NST3 encodes a known regulator of secondary cell wall formation in xylem fibers [34,35]. Interestingly, the qRT-PCR data also indicated a similar expression pattern between PXC1 and WOX4, with the highest level of transcript observed in young stem (Additional file 4G and H). CLE41 and CLE44 both encode the B-type CLE peptides that act as the ligands for the TDIF-PXY/TDR signal transduction pathway [31]. As previously reported, the CLE41 transcript was found to be mainly associated with the phloem fraction (Additional file 4E) [13]. This fraction may, however, include some cambium cells as a result of the sample collection (peeling) method used [13]. CLE44 transcript appeared more evenly distributed among the tissue fractions, with a significantly lower level of transcripts in the xylem tissue (Additional file 4F), which is consistent with the recent report of phloem-specific expression of CLE44::GUS[36]. To summarize the expression patterns described above, a heat map was generated using the qPCR data. Strikingly, the heat map highlighted the similarities between PXC1 and WOX4 in vascular tissues (FigureĀ 4).


The Arabidopsis LRR-RLK, PXC1, is a regulator of secondary wall formation correlated with the TDIF-PXY/TDR-WOX4 signaling pathway.

Wang J, Kucukoglu M, Zhang L, Chen P, Decker D, Nilsson O, Jones B, Sandberg G, Zheng B - BMC Plant Biol. (2013)

A heat-map (log transformed) of qRT-PCR gene expression data for main regulators of vascular development in 5-week old wild-type Arabidopsis. Stem1 denoted the base of main inflorescence stem 10 cm in height above the uppermost rosette leaf and stem2 denoted the base of main inflorescence stem 30 cm in height above the uppermost rosette leaf. Phloem and xylem were ontained by peeling method.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3716795&req=5

Figure 4: A heat-map (log transformed) of qRT-PCR gene expression data for main regulators of vascular development in 5-week old wild-type Arabidopsis. Stem1 denoted the base of main inflorescence stem 10 cm in height above the uppermost rosette leaf and stem2 denoted the base of main inflorescence stem 30 cm in height above the uppermost rosette leaf. Phloem and xylem were ontained by peeling method.
Mentions: Because the strongest predicted links were between PXC1 and PXY/TDR, we concentrated our efforts on this gene. To further investigate the function of PXC1 in vascular development, transcript levels of PXC1 were determined in parallel with seven known regulators of vascular development in different plant tissues including the leaf lamina (as a control), petiole, young inflorescence stem, old inflorescence stem and hypocotyl. Our data showed that the transcripts for PXY were most abundant in the xylem fraction of hypocotyls, with levels increasing in older inflorescence stems (Additional file 4C). Expression patterns for HB8, HB15 (HOMEOBOX GENE 15) and NST3 (NAC TRANSCRIPTION FACTOR3) were similar to those observed for PXY (Additional file 4A, B and D). HB8 and HB15 are both recognized as molecular markers of procambial cells [32,33] and NST3 encodes a known regulator of secondary cell wall formation in xylem fibers [34,35]. Interestingly, the qRT-PCR data also indicated a similar expression pattern between PXC1 and WOX4, with the highest level of transcript observed in young stem (Additional file 4G and H). CLE41 and CLE44 both encode the B-type CLE peptides that act as the ligands for the TDIF-PXY/TDR signal transduction pathway [31]. As previously reported, the CLE41 transcript was found to be mainly associated with the phloem fraction (Additional file 4E) [13]. This fraction may, however, include some cambium cells as a result of the sample collection (peeling) method used [13]. CLE44 transcript appeared more evenly distributed among the tissue fractions, with a significantly lower level of transcripts in the xylem tissue (Additional file 4F), which is consistent with the recent report of phloem-specific expression of CLE44::GUS[36]. To summarize the expression patterns described above, a heat map was generated using the qPCR data. Strikingly, the heat map highlighted the similarities between PXC1 and WOX4 in vascular tissues (FigureĀ 4).

Bottom Line: Expression profiling using qPCR and promoter:reporter lines indicated that all three PXC genes are associated with the vasculature.Shifting pxc1 mutants from long-days to short-days showed that loss of the gene led to a dramatic reduction in secondary wall formation in xylem fibers.Transcript analysis of mutants for a variety of secondary cell wall-associated genes, including PXY/TDR indicated that the pathways mediated by PXC1 connect with those mediated by the TDIF-PXY/TDR-WOX4 system.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Environmental Science and Engineering, Tianjin University, 300072 Tianjin, China.

ABSTRACT

Background: Although a number of leucine-rich repeat receptor-like kinase-encoding genes (LRR-RLKs) have been identified in plants, a functional role has been determined for only a few. Recent studies have demonstrated that an LRR-RLK, PXY/TDR, is important for the process of secondary vascular development. Other studies have indicated that PXY/TDR is unlikely to be the sole LRR-RLK involved in this complex process.

Results: In this study, in silico analyses led to the identification of three Arabidopsis LRR-RLK genes (PXY-correlated; PXC1, 2, 3) with transcript accumulation profiles that correlated strongly with several key regulators of vascular development, including PXY/TDR, HB-8, REV, and CLE41. Expression profiling using qPCR and promoter:reporter lines indicated that all three PXC genes are associated with the vasculature. One in particular, PXC1 (At2g36570), had a strong correlation with PXY/TDR. Shifting pxc1 mutants from long-days to short-days showed that loss of the gene led to a dramatic reduction in secondary wall formation in xylem fibers. Transcript analysis of mutants for a variety of secondary cell wall-associated genes, including PXY/TDR indicated that the pathways mediated by PXC1 connect with those mediated by the TDIF-PXY/TDR-WOX4 system.

Conclusions: The data indicate that the LRR-RLK, PXC1 is involved in secondary cell wall formation in xylem fibers. Whereas further study is needed to identify the ligands and mode of action of the PXC1 protein, it is clear from this work that similarly to the shoot apical meristem (SAM), secondary vascular development requires contributions from a number of LRR-RLKs.

Show MeSH
Related in: MedlinePlus