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Multiple roles of the transcription factor AtMYBR1/AtMYB44 in ABA signaling, stress responses, and leaf senescence.

Jaradat MR, Feurtado JA, Huang D, Lu Y, Cutler AJ - BMC Plant Biol. (2013)

Bottom Line: MYBR1 appears to exhibit partially redundant functions with AtMYBR2 (MYB77) and double mybr1 X mybr2 mutants exhibited stronger senescence and stress related phenotypes than single mybr1 and mybr2 mutants.MYBR1 is a negative regulator of ABA, stress, wounding responses and blocks senescence.It appears to have a homeostatic function to maintain growth processes in the event of physical damage or stress.

View Article: PubMed Central - HTML - PubMed

Affiliation: Plant Biotechnology Institute, National Research Council of Canada, 110 Gymnasium Place, Saskatoon S7N 0W9, Canada. adrian.cutler@nrc-cnrc.gc.ca.

ABSTRACT

Background: The transcription factor AtMYBR1 (MYB44) is a member of the MYB family of transcription factors and is expressed throughout the plant life cycle and especially in senescing and wounded leaves. It has previously been shown to be involved in responses to abiotic stress and is regulated by phosphorylation.

Results: When MYBR1 was over-expressed under the control of the constitutive 35S promoter in Arabidopsis thaliana (OxMYBR1), leaf senescence was delayed. In contrast loss-of-function mybr1 plants showed more rapid chlorophyll loss and senescence. The MYBR1 promoter strongly drove β-GLUCURONIDASE reporter gene expression in tissues immediately after wounding and many wounding/pathogenesis genes were downregulated in OxMYBR1. OxMYBR1 plants were more susceptible to injury under water stress than wildtype, which was correlated with suppression of many ABA inducible stress genes in OxMYBR1. Conversely, mybr1 plants were more tolerant of water stress and exhibited reduced rates of water loss from leaves. MYBR1 physically interacted with ABA receptor PYR1-LIKE8 (PYL8) suggesting a direct involvement of MYBR1 in early ABA signaling. MYBR1 appears to exhibit partially redundant functions with AtMYBR2 (MYB77) and double mybr1 X mybr2 mutants exhibited stronger senescence and stress related phenotypes than single mybr1 and mybr2 mutants.

Conclusions: MYBR1 is a negative regulator of ABA, stress, wounding responses and blocks senescence. It appears to have a homeostatic function to maintain growth processes in the event of physical damage or stress.

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AtMYBR1 promoter drives GUS expression during abiotic stress, floral organ abscission and mechanical wounding. Histochemical localization of GUS activity was performed by staining with X-gluc for different time intervals as described below and in Methods. Panel (A) Significant reduction of GUS expression in leaves after drought stress. However, intense GUS expression in roots was similar to control. (B) A closed flower was opened manually by forceps before GUS staining was performed. (C) A fully opened flower. (B) and (C) No GUS expression was found on pedicel at the point where the sepal, petal and anther join (shown by arrows). (D) and (E) In contrast, intense GUS expression was observed at pedicel connecting sites of floral organs after abscission (arrowheads). (E) A silique fully abscised with floral organs, was stained briefly (2 h) for GUS. Magnification of the connections between floral organs and pedicel shows GUS expression only at attachment sites on pedicel. Panel (F) Leaves were wounded with hemostats. Intense MYBR1 promoter driven GUS expression was observed around the wound relative to control.
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Figure 4: AtMYBR1 promoter drives GUS expression during abiotic stress, floral organ abscission and mechanical wounding. Histochemical localization of GUS activity was performed by staining with X-gluc for different time intervals as described below and in Methods. Panel (A) Significant reduction of GUS expression in leaves after drought stress. However, intense GUS expression in roots was similar to control. (B) A closed flower was opened manually by forceps before GUS staining was performed. (C) A fully opened flower. (B) and (C) No GUS expression was found on pedicel at the point where the sepal, petal and anther join (shown by arrows). (D) and (E) In contrast, intense GUS expression was observed at pedicel connecting sites of floral organs after abscission (arrowheads). (E) A silique fully abscised with floral organs, was stained briefly (2 h) for GUS. Magnification of the connections between floral organs and pedicel shows GUS expression only at attachment sites on pedicel. Panel (F) Leaves were wounded with hemostats. Intense MYBR1 promoter driven GUS expression was observed around the wound relative to control.

Mentions: A 2.7 kb promoter fragment of MYBR1 including the 5′UTR was fused to the β-GLUCURONIDASE (GUS) reporter gene (MYBR1pro:GUS) and the expression of MYBR1 was examined histochemically. GUS staining was performed on homozygous T2 and T3 plants. In 13 d old seedlings (Additional file 1: Figure S3A), GUS expression driven by the MYBR1 promoter was observed in cotyledons and true leaves. In contrast to very high GUS expression in cotyledons, GUS expression was lower in younger true leaves relative to older leaves and was absent in the newly emerged leaves. Intriguingly, GUS expression was observed in patches in younger leaves and was absent around the vascular regions of both older and younger leaves hinting that MYBR1 could be involved in senescence since this pattern was reminiscent of the development of visible senescence in leaves reviewed in [9]. Under normal conditions, expression of GUS was also observed in hydathodes of all leaf margins as well as embryo, suspensor, endosperm, root, stigma, sepal, petal and anther filament but was absent in stem, cauline leaf, anther, silique and testa (Figure 4A, C, D and E and Additional file 1: Figure S3). GUS expression was observed in embryo and endosperm dissected from siliques at developmental stages from 6–18 DPA as well as from dry and imbibed (30 min – 99 h) mature seeds (Additional file 1: Figure S3B and S3C). The intensity of GUS staining increased with development in embryos but remained constant in endosperm except at 6 DPA when the GUS expression was lower. GUS expression was high and remained constant in embryos collected from dry seeds and seeds imbibed up to 24 h but declined subsequently. GUS expression in endosperm of dry and imbibed seeds remained high.


Multiple roles of the transcription factor AtMYBR1/AtMYB44 in ABA signaling, stress responses, and leaf senescence.

Jaradat MR, Feurtado JA, Huang D, Lu Y, Cutler AJ - BMC Plant Biol. (2013)

AtMYBR1 promoter drives GUS expression during abiotic stress, floral organ abscission and mechanical wounding. Histochemical localization of GUS activity was performed by staining with X-gluc for different time intervals as described below and in Methods. Panel (A) Significant reduction of GUS expression in leaves after drought stress. However, intense GUS expression in roots was similar to control. (B) A closed flower was opened manually by forceps before GUS staining was performed. (C) A fully opened flower. (B) and (C) No GUS expression was found on pedicel at the point where the sepal, petal and anther join (shown by arrows). (D) and (E) In contrast, intense GUS expression was observed at pedicel connecting sites of floral organs after abscission (arrowheads). (E) A silique fully abscised with floral organs, was stained briefly (2 h) for GUS. Magnification of the connections between floral organs and pedicel shows GUS expression only at attachment sites on pedicel. Panel (F) Leaves were wounded with hemostats. Intense MYBR1 promoter driven GUS expression was observed around the wound relative to control.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4219380&req=5

Figure 4: AtMYBR1 promoter drives GUS expression during abiotic stress, floral organ abscission and mechanical wounding. Histochemical localization of GUS activity was performed by staining with X-gluc for different time intervals as described below and in Methods. Panel (A) Significant reduction of GUS expression in leaves after drought stress. However, intense GUS expression in roots was similar to control. (B) A closed flower was opened manually by forceps before GUS staining was performed. (C) A fully opened flower. (B) and (C) No GUS expression was found on pedicel at the point where the sepal, petal and anther join (shown by arrows). (D) and (E) In contrast, intense GUS expression was observed at pedicel connecting sites of floral organs after abscission (arrowheads). (E) A silique fully abscised with floral organs, was stained briefly (2 h) for GUS. Magnification of the connections between floral organs and pedicel shows GUS expression only at attachment sites on pedicel. Panel (F) Leaves were wounded with hemostats. Intense MYBR1 promoter driven GUS expression was observed around the wound relative to control.
Mentions: A 2.7 kb promoter fragment of MYBR1 including the 5′UTR was fused to the β-GLUCURONIDASE (GUS) reporter gene (MYBR1pro:GUS) and the expression of MYBR1 was examined histochemically. GUS staining was performed on homozygous T2 and T3 plants. In 13 d old seedlings (Additional file 1: Figure S3A), GUS expression driven by the MYBR1 promoter was observed in cotyledons and true leaves. In contrast to very high GUS expression in cotyledons, GUS expression was lower in younger true leaves relative to older leaves and was absent in the newly emerged leaves. Intriguingly, GUS expression was observed in patches in younger leaves and was absent around the vascular regions of both older and younger leaves hinting that MYBR1 could be involved in senescence since this pattern was reminiscent of the development of visible senescence in leaves reviewed in [9]. Under normal conditions, expression of GUS was also observed in hydathodes of all leaf margins as well as embryo, suspensor, endosperm, root, stigma, sepal, petal and anther filament but was absent in stem, cauline leaf, anther, silique and testa (Figure 4A, C, D and E and Additional file 1: Figure S3). GUS expression was observed in embryo and endosperm dissected from siliques at developmental stages from 6–18 DPA as well as from dry and imbibed (30 min – 99 h) mature seeds (Additional file 1: Figure S3B and S3C). The intensity of GUS staining increased with development in embryos but remained constant in endosperm except at 6 DPA when the GUS expression was lower. GUS expression was high and remained constant in embryos collected from dry seeds and seeds imbibed up to 24 h but declined subsequently. GUS expression in endosperm of dry and imbibed seeds remained high.

Bottom Line: MYBR1 appears to exhibit partially redundant functions with AtMYBR2 (MYB77) and double mybr1 X mybr2 mutants exhibited stronger senescence and stress related phenotypes than single mybr1 and mybr2 mutants.MYBR1 is a negative regulator of ABA, stress, wounding responses and blocks senescence.It appears to have a homeostatic function to maintain growth processes in the event of physical damage or stress.

View Article: PubMed Central - HTML - PubMed

Affiliation: Plant Biotechnology Institute, National Research Council of Canada, 110 Gymnasium Place, Saskatoon S7N 0W9, Canada. adrian.cutler@nrc-cnrc.gc.ca.

ABSTRACT

Background: The transcription factor AtMYBR1 (MYB44) is a member of the MYB family of transcription factors and is expressed throughout the plant life cycle and especially in senescing and wounded leaves. It has previously been shown to be involved in responses to abiotic stress and is regulated by phosphorylation.

Results: When MYBR1 was over-expressed under the control of the constitutive 35S promoter in Arabidopsis thaliana (OxMYBR1), leaf senescence was delayed. In contrast loss-of-function mybr1 plants showed more rapid chlorophyll loss and senescence. The MYBR1 promoter strongly drove β-GLUCURONIDASE reporter gene expression in tissues immediately after wounding and many wounding/pathogenesis genes were downregulated in OxMYBR1. OxMYBR1 plants were more susceptible to injury under water stress than wildtype, which was correlated with suppression of many ABA inducible stress genes in OxMYBR1. Conversely, mybr1 plants were more tolerant of water stress and exhibited reduced rates of water loss from leaves. MYBR1 physically interacted with ABA receptor PYR1-LIKE8 (PYL8) suggesting a direct involvement of MYBR1 in early ABA signaling. MYBR1 appears to exhibit partially redundant functions with AtMYBR2 (MYB77) and double mybr1 X mybr2 mutants exhibited stronger senescence and stress related phenotypes than single mybr1 and mybr2 mutants.

Conclusions: MYBR1 is a negative regulator of ABA, stress, wounding responses and blocks senescence. It appears to have a homeostatic function to maintain growth processes in the event of physical damage or stress.

Show MeSH
Related in: MedlinePlus