Abstract
In response to environmental challenges, plant cells activate several signaling pathways that trigger the expression of transcription factors. Arabidopsis MYB60 was reported to be involved in stomatal regulation under drought conditions. Here, two splice variants of the MYB60 gene are shown to play a crucial role in stomatal movement. This role was demonstrated by over-expressing each variant, resulting in enhanced sensitivity to water deficit stress. The MYB60 splice variants, despite the fact that one of which lacks the first two exons encoding the first MYB DNA binding domain, both localize to the nucleus and promote guard cell deflation in response to water deficit. Moreover, MYB60 expression is increased in response to a low level of ABA and decreased in response to high level of ABA. At initial stage of drought stress, the plant system may modulate the root growth behavior by regulating MYB60 expression, thus promotes root growth for increased water uptake. In contrast, severe drought stress inhibits the expression of the MYB60 gene, resulting in stomatal closure and root growth inhibition. Taken together, these data indicate that MYB60 plays a dual role in abiotic stress responses in Arabidopsis through its involvement in stomatal regulation and root growth.
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Acknowledgments
This work was supported by a grant from the Korea Research Foundation to Hojoung Lee (2009; Grant #2011-0003726) in part by a grant from the Korea Research Foundation to Suk-Whan Hong (grant #2011-0003259 and #2011-0018393). The authors express their gratitude to Dr. Cominelli for providing seeds of the myb60 knock-out line.
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J. E. Oh and Y. Kwon authors contributed equally.
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11103_2011_9796_MOESM1_ESM.jpg
Figure S1. Histochemical GUS staining of AtMYB60pro∷GUS plants. Expression of MYB60 was examined in the whole organism. MYB60 promoter regions of varying lengths were cloned in front of the GUS gene and inserted into wild-type plants. Six-week-old plants were stained with GUS solution overnight, and chlorophyll was removed by treatment with 70% ethanol. MYB60proF1, MYB60proF2, and MYB60proF3 contain ~1.2 kb, ~0.8 kb, and ~0.4 kb of the MYB60 upstream region, respectively. (JPEG 70 kb)
11103_2011_9796_MOESM2_ESM.jpg
Figure S2. Drought response of the wild-type and myb60 knock-out plants. Root architecture of Col-0 and myb60 knock-out plants grown on media supplemented with mannitol. Seeds were germinated on MS medium and subsequent 5-day-old seedlings were transferred to medium supplemented with mannitol and allowed to grow for 10 additional days. (JPEG 47 kb)
11103_2011_9796_MOESM3_ESM.jpg
Figure S3. Model for the dual function of MYB60. Under normal conditions, MYB60 is expressed at substantial levels and mediates stomatal opening. (A) Under mild drought conditions, low levels of ABA increase the level of the MYB60 transcripts. This leads to an alteration in the level of local flavonoids, resulting in the modulation of polar auxin transport. Overall root growth is affected. In the initial stage of stress condition, the plant system may modulate the behavior of root growth by regulating the expression of MYB60. In this manner, the plant may promote root growth in order to increase water uptake as much as possible. (B) Under severe drought conditions, MYB60 is down-regulated in the guard cells. Stomatal opening is no longer activated and increased ABA triggers stomatal closure. Severe drought stress blocks MYB60 expression, resulting in stomatal closure and root growth inhibition. (JPEG 34 kb)
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Oh, J.E., Kwon, Y., Kim, J.H. et al. A dual role for MYB60 in stomatal regulation and root growth of Arabidopsis thaliana under drought stress. Plant Mol Biol 77, 91–103 (2011). https://doi.org/10.1007/s11103-011-9796-7
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DOI: https://doi.org/10.1007/s11103-011-9796-7