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A Systematic View of the MLO Family in Rice Suggests Their Novel Roles in Morphological Development, Diurnal Responses, the Light-Signaling Pathway, and Various Stress Responses

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ABSTRACT

The Mildew resistance Locus O (MLO) family is unique to plants, containing genes that were initially identified as a susceptibility factor to powdery mildew pathogens. However, little is known about the roles and functional diversity of this family in rice, a model crop plant. The rice genome has 12 potential MLO family members. To achieve systematic functional assignments, we performed a phylogenomic analysis by integrating meta-expression data obtained from public sources of microarray data and real-time expression data into a phylogenic tree. Subsequently, we identified 12 MLO genes with various tissue-preferred patterns, including leaf, root, pollen, and ubiquitous expression. This suggested their functional diversity for morphological agronomic traits. We also used these integrated transcriptome data within a phylogenetic context to estimate the functional redundancy or specificity among OsMLO family members. Here, OsMLO12 showed preferential expression in mature pollen; OsMLO4, in the root tips; OsMLO10, throughout the roots except at the tips; and OsMLO8, expression preferential to the leaves and trinucleate pollen. Of particular interest to us was the diurnal expression of OsMLO1, OsMLO3, and OsMLO8, which indicated that they are potentially significant in responses to environmental changes. In osdxr mutants that show defects in the light response, OsMLO1, OsMLO3, OsMLO8, and four calmodulin genes were down-regulated. This finding provides insight into the novel functions of MLO proteins associated with the light-responsive methylerythritol 4-phosphate pathway. In addition, abiotic stress meta-expression data and real-time expression analysis implied that four and five MLO genes in rice are associated with responses to heat and cold stress, respectively. Upregulation of OsMLO3 by Magnaporthe oryzae infection further suggested that this gene participates in the response to pathogens. Our analysis has produced fundamental information that will enhance future studies of the diverse developmental or physiological phenomena mediated by the MLO family in this model plant system.

No MeSH data available.


Related in: MedlinePlus

Heatmap for expression patterns of OsCML genes in wild-type (WT/DXR) rice and osdxr mutant. (A) Expression analysis of 4 OsCML genes using Agilent 60K microarray data for WT vs. osdxr knockout line. (B) Downregulation of OsCML genes in osdxr mutant demonstrated by real-time PCR analysis. **p < 0.01; *0.01 < p < 0.05.
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Figure 6: Heatmap for expression patterns of OsCML genes in wild-type (WT/DXR) rice and osdxr mutant. (A) Expression analysis of 4 OsCML genes using Agilent 60K microarray data for WT vs. osdxr knockout line. (B) Downregulation of OsCML genes in osdxr mutant demonstrated by real-time PCR analysis. **p < 0.01; *0.01 < p < 0.05.

Mentions: The MLO proteins interact with calmodulin as the second messenger to transfer a signal forward to downstream pathways (Kim et al., 2002a,b; Stein and Somerville, 2002). To investigate whether the diurnal response-dependent OsMLOs function with calmodulin proteins, we examined the differential expression of calmodulin (CaM) and CaM-like (CML), searching for genes with log2-fold changes >1.8 and p-values <0.05 in the osdxr mutant (Table S2). Subsequent analysis of the microarray data presented four CML genes—OsCML1, OsCML16, OsCML24, and OsCML28—with decreased expression in that mutant (Figure 6A). Real-time PCR analysis also confirmed that all four were significantly down-regulated in osdxr (Figure 6B). Therefore, we propose that these OsCML genes would be primary targets for studying functional relationships among diurnal response-dependent OsMLOs.


A Systematic View of the MLO Family in Rice Suggests Their Novel Roles in Morphological Development, Diurnal Responses, the Light-Signaling Pathway, and Various Stress Responses
Heatmap for expression patterns of OsCML genes in wild-type (WT/DXR) rice and osdxr mutant. (A) Expression analysis of 4 OsCML genes using Agilent 60K microarray data for WT vs. osdxr knockout line. (B) Downregulation of OsCML genes in osdxr mutant demonstrated by real-time PCR analysis. **p < 0.01; *0.01 < p < 0.05.
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Related In: Results  -  Collection

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Figure 6: Heatmap for expression patterns of OsCML genes in wild-type (WT/DXR) rice and osdxr mutant. (A) Expression analysis of 4 OsCML genes using Agilent 60K microarray data for WT vs. osdxr knockout line. (B) Downregulation of OsCML genes in osdxr mutant demonstrated by real-time PCR analysis. **p < 0.01; *0.01 < p < 0.05.
Mentions: The MLO proteins interact with calmodulin as the second messenger to transfer a signal forward to downstream pathways (Kim et al., 2002a,b; Stein and Somerville, 2002). To investigate whether the diurnal response-dependent OsMLOs function with calmodulin proteins, we examined the differential expression of calmodulin (CaM) and CaM-like (CML), searching for genes with log2-fold changes >1.8 and p-values <0.05 in the osdxr mutant (Table S2). Subsequent analysis of the microarray data presented four CML genes—OsCML1, OsCML16, OsCML24, and OsCML28—with decreased expression in that mutant (Figure 6A). Real-time PCR analysis also confirmed that all four were significantly down-regulated in osdxr (Figure 6B). Therefore, we propose that these OsCML genes would be primary targets for studying functional relationships among diurnal response-dependent OsMLOs.

View Article: PubMed Central - PubMed

ABSTRACT

The Mildew resistance Locus O (MLO) family is unique to plants, containing genes that were initially identified as a susceptibility factor to powdery mildew pathogens. However, little is known about the roles and functional diversity of this family in rice, a model crop plant. The rice genome has 12 potential MLO family members. To achieve systematic functional assignments, we performed a phylogenomic analysis by integrating meta-expression data obtained from public sources of microarray data and real-time expression data into a phylogenic tree. Subsequently, we identified 12 MLO genes with various tissue-preferred patterns, including leaf, root, pollen, and ubiquitous expression. This suggested their functional diversity for morphological agronomic traits. We also used these integrated transcriptome data within a phylogenetic context to estimate the functional redundancy or specificity among OsMLO family members. Here, OsMLO12 showed preferential expression in mature pollen; OsMLO4, in the root tips; OsMLO10, throughout the roots except at the tips; and OsMLO8, expression preferential to the leaves and trinucleate pollen. Of particular interest to us was the diurnal expression of OsMLO1, OsMLO3, and OsMLO8, which indicated that they are potentially significant in responses to environmental changes. In osdxr mutants that show defects in the light response, OsMLO1, OsMLO3, OsMLO8, and four calmodulin genes were down-regulated. This finding provides insight into the novel functions of MLO proteins associated with the light-responsive methylerythritol 4-phosphate pathway. In addition, abiotic stress meta-expression data and real-time expression analysis implied that four and five MLO genes in rice are associated with responses to heat and cold stress, respectively. Upregulation of OsMLO3 by Magnaporthe oryzae infection further suggested that this gene participates in the response to pathogens. Our analysis has produced fundamental information that will enhance future studies of the diverse developmental or physiological phenomena mediated by the MLO family in this model plant system.

No MeSH data available.


Related in: MedlinePlus