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.
SummaryThe Arabidopsis hot2 mutant was originally identified based on its lack of thermotolerance, but pleiotropic abnormal phenotypes are also exhibited under normal conditions, including semi-dwarfism, ethylene overproduction and aberrant cell shape with incomplete cell walls. Here we present additional characterization of the hot2 mutant, and the map-based cloning of HOT2. Mutants of hot2 had an aberrant tolerance to salt and drought stresses, and accumulated high levels of Na þ in cells under either normal or NaCl stress conditions. Expression of the stress-inducible COR15A and KIN1 gene in hot2 mutants in response to increased NaCl concentrations was normal. HOT2 encoded a chitinase-like protein (AtCTL1) that has not previously been shown to be involved in tolerance to salt stress. Ten-day-old seedlings of wild-type plants exhibited constitutive expression of the AtCTL1 transcript, the level of which was unaffected by treatment with NaCl, mannitol or mild heat. These observations provide genetic evidence that a chitinase-like protein prevents the overaccumulation of Na þ ions, thereby contributing to the salt tolerance in Arabidopsis. A possible role for this chitinase-like protein in Arabidopsis tolerance to abiotic stress is discussed.
Summary
During growth and development, plants undergo a series of phase transitions from the juvenile‐to‐adult vegetative phase to the reproductive phase. In Arabidopsis, vegetative phase transitions and flowering are regulated by SQUAMOSA PROMOTER BINDING PROTEIN‐LIKE (SPL) factors. SPL mRNAs are post‐transcriptionally regulated by miR156 in an age‐dependent manner; however, the role of other mechanisms in this process is not known. In this study, we demonstrate that the HAG1/GCN5‐ and PRZ1/ADA2b‐containing SAGA‐like histone acetyltransferase (HAT) complex directly controls the transcription of SPLs and determines the time for juvenile‐to‐adult phase transition. Thus, epigenetic control by the SAGA‐like HAT complex determines the transcriptional output of SPLs, which might be a prerequisite for the subsequent post‐transcriptional regulation by miR156. Importantly, this epigenetic control mechanism is also crucial for miR156‐independent induction of SPLs and acceleration of phase transition by light and photoperiod or during post‐embryonic growth.
In an attempt to understand the complex regulatory mechanisms underlying sucrose-induced flavonoid biosynthesis, we examined several Arabidopsis mutants with altered anthocyanin accumulation. We determined that disruption of ethylene signaling results in a dramatic increase in sucrose-induced anthocyanin accumulation. Furthermore, we investigated why the ein2-1 (ethylene insensitive) Arabidopsis mutant accumulates higher levels of anthocyanin in response to sucrose than wild-type Arabidopsis. An increased level of PAP1 transcript in the ein2-1 mutant appears to be the main factor responsible for the increased accumulation of anthocyanin in response to sucrose. Therefore, our results indicate that the ethylene signaling pathway plays a negative role in sucrose-induced anthocyanin accumulation. We believe that the explanation for this observation may be related to the initiation of the senescence program in plants.
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