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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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Transcript level changes of genes involved in TDIF/PXY/WOX4 pathway and vascular development markers in wild-type Arabidopsis and various mutants and overexpressors. (A) Gene expression levels analyzed by qPCR in the hypocotyls of 5-week-old wild-type Arabidopsis and mutants under long-day conditions; (B) Change in gene expression level in the basal stem part of two 51-day-old PXC1 mutants after the long-day to short-day shifting experiment; (C) Relative CLE44 expression level measured by qRT-PCR in Col-0 and three CLE44 ox plants with inflorescence stems as tall as 15 cm; (D) Relative expression level of marker genes in wild-type and three CLE44 ox lines with inflorescence stems as tall as 15 cm.
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Figure 7: Transcript level changes of genes involved in TDIF/PXY/WOX4 pathway and vascular development markers in wild-type Arabidopsis and various mutants and overexpressors. (A) Gene expression levels analyzed by qPCR in the hypocotyls of 5-week-old wild-type Arabidopsis and mutants under long-day conditions; (B) Change in gene expression level in the basal stem part of two 51-day-old PXC1 mutants after the long-day to short-day shifting experiment; (C) Relative CLE44 expression level measured by qRT-PCR in Col-0 and three CLE44 ox plants with inflorescence stems as tall as 15 cm; (D) Relative expression level of marker genes in wild-type and three CLE44 ox lines with inflorescence stems as tall as 15 cm.

Mentions: qPCR analysis of PXY, PXC1, CLE41, CLE44 and WOX4 expression was analyzed in the pxy/tdr, pxc1, cle41, cle44 and wox4 mutants. Transcript abundances of PXY and CLE41 were not dramatically affected in the pxy/tdr, pxc1 and wox4 knockout lines (Figure 7A). The transcript level of PXC1, WOX4 and CLE44 were significantly increased in pxy, pxc1 and wox4 mutants compared to the wild-type (Figure 7A). The elevated expression level of WOX4 in the pxy background was unexpected since that WOX4 is a key downstream target of the TDIF-PXY/TDR signaling pathway [13]. This result indicated a possibility that PXY might not be the only receptor acting upstream of WOX4. Meanwhile, instead of young seedlings [13], 5-week-old hypocotyls, which contain more secondary growth, were used in this study and the implication of PXY/TDR in xylem development has not been investigated in details. The dramatic increase in PXC1 transcripts occurred in the pxy and wox4 knockout mutants indicated that either the PXY-WOX4 pathway negatively regulate the expression of PXC1, or that PXC1 is upregulated in these mutants as a compensatory measure (Figure 7A). These data also suggested that the signal transduction pathways mediated by PXY and PXC1 are at least partly overlapping. However, it is hard to specify the position of PXC1 relative to the TDIF/PXY/WOX4 pathway because we could not judge which alterations in gene expression resulting from forward responses or feedback responses.


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)

Transcript level changes of genes involved in TDIF/PXY/WOX4 pathway and vascular development markers in wild-type Arabidopsis and various mutants and overexpressors. (A) Gene expression levels analyzed by qPCR in the hypocotyls of 5-week-old wild-type Arabidopsis and mutants under long-day conditions; (B) Change in gene expression level in the basal stem part of two 51-day-old PXC1 mutants after the long-day to short-day shifting experiment; (C) Relative CLE44 expression level measured by qRT-PCR in Col-0 and three CLE44 ox plants with inflorescence stems as tall as 15 cm; (D) Relative expression level of marker genes in wild-type and three CLE44 ox lines with inflorescence stems as tall as 15 cm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: Transcript level changes of genes involved in TDIF/PXY/WOX4 pathway and vascular development markers in wild-type Arabidopsis and various mutants and overexpressors. (A) Gene expression levels analyzed by qPCR in the hypocotyls of 5-week-old wild-type Arabidopsis and mutants under long-day conditions; (B) Change in gene expression level in the basal stem part of two 51-day-old PXC1 mutants after the long-day to short-day shifting experiment; (C) Relative CLE44 expression level measured by qRT-PCR in Col-0 and three CLE44 ox plants with inflorescence stems as tall as 15 cm; (D) Relative expression level of marker genes in wild-type and three CLE44 ox lines with inflorescence stems as tall as 15 cm.
Mentions: qPCR analysis of PXY, PXC1, CLE41, CLE44 and WOX4 expression was analyzed in the pxy/tdr, pxc1, cle41, cle44 and wox4 mutants. Transcript abundances of PXY and CLE41 were not dramatically affected in the pxy/tdr, pxc1 and wox4 knockout lines (Figure 7A). The transcript level of PXC1, WOX4 and CLE44 were significantly increased in pxy, pxc1 and wox4 mutants compared to the wild-type (Figure 7A). The elevated expression level of WOX4 in the pxy background was unexpected since that WOX4 is a key downstream target of the TDIF-PXY/TDR signaling pathway [13]. This result indicated a possibility that PXY might not be the only receptor acting upstream of WOX4. Meanwhile, instead of young seedlings [13], 5-week-old hypocotyls, which contain more secondary growth, were used in this study and the implication of PXY/TDR in xylem development has not been investigated in details. The dramatic increase in PXC1 transcripts occurred in the pxy and wox4 knockout mutants indicated that either the PXY-WOX4 pathway negatively regulate the expression of PXC1, or that PXC1 is upregulated in these mutants as a compensatory measure (Figure 7A). These data also suggested that the signal transduction pathways mediated by PXY and PXC1 are at least partly overlapping. However, it is hard to specify the position of PXC1 relative to the TDIF/PXY/WOX4 pathway because we could not judge which alterations in gene expression resulting from forward responses or feedback responses.

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