Genetic manipulation of protein phosphatase 2A affects multiple agronomic traits and physiological parameters in potato (Solanum tuberosum).

In this study, agronomic and functional characteristics of potato (Solanum tuberosum ) plants constitutively overexpressing the protein phosphatase 2A (PP2A) catalytic subunit StPP2Ac2b (StPP2Ac2b-OE) were evaluated. StPP2Ac2b-OE plants display reduced vegetative growth, tuber yield and tuber weight under well-watered and drought conditions. Leaves of StPP2Ac2b-OE plants show an increased rate of water loss, associated with an impaired ability to close stomata in response to abscisic acid. StPP2Ac2b-OE lines exhibit larger stomatal size and reduced stomatal density. These altered stomatal characteristics might be responsible for the impaired stomatal closure and the elevated transpiration rates, ultimately leading to increased sensitivity to water-deficit stress and greater yield loss under drought conditions. Overexpression of StPP2Ac2b accelerates senescence in response to water-deficit stress, which could also contribute to the increased sensitivity to drought. Actively photosynthesising leaves of StPP2Ac2b-OE plants exhibit elevated levels of carbohydrates and a down-regulation of the sucrose transporter StSWEET11 , suggesting a reduced sucrose export from leaves to developing tubers. This effect, combined with the hindered vegetative development, may contribute to the reduced tuber weight and yield in StPP2Ac2b-OE plants. These findings offer novel insights into the physiological functions of PP2A in potato plants and provide valuable information for enhancing potato productivity by modulating the expression of StPP2Ac2b .

The protein phosphatase 2A catalytic subunit StPP2Ac2b enhances susceptibility to Phytophthora infestans and senescence in potato.

The serine/threonine protein phosphatases type 2A (PP2A) are involved in several physiological responses in plants, playing important roles in developmental programs, stress responses and hormone signaling. Six PP2A catalytic subunits (StPP2Ac) were identified in cultivated potato. Transgenic potato plants constitutively overexpressing the catalytic subunit StPP2Ac2b (StPP2Ac2b-OE) were developed to determine its physiological roles. The response of StPP2Ac2b-OE plants to the oomycete Phytophthora infestans, the causal agent of late blight, was evaluated. We found that overexpression of StPP2Ac2b enhances susceptibility to the pathogen. Further bioinformatics, biochemical, and molecular analyses revealed that StPP2Ac2b positively regulates developmental and pathogen-induced senescence, and that P. infestans infection promotes senescence, most likely through induction of StPP2Ac2b expression.

The protein phosphatase 2A catalytic subunit StPP2Ac2b is involved in the control of potato tuber sprouting and source-sink balance in tubers and sprouts.

Sprouting negatively affects the quality of stored potato tubers. Understanding the molecular mechanisms that control this process is important for the development of potato varieties with desired sprouting characteristics. Serine/threonine protein phosphatase type 2A (PP2A) has been implicated in several developmental programs and stress responses in plants. PP2A comprises a catalytic (PP2Ac), a scaffolding (A), and a regulatory (B) subunit. In cultivated potato, six PP2Ac isoforms were identified, named StPP2Ac1, 2a, 2b, 3, 4, and 5. In this study we evaluated the sprouting behavior of potato tubers overexpressing the catalytic subunit 2b (StPP2Ac2b-OE). The onset of sprouting and initial sprout elongation is significantly delayed in StPP2Ac2b-OE tubers; however, sprout growth is accelerated during the late stages of development, due to a high degree of branching. StPP2Ac2b-OE tubers also exhibit a pronounced loss of apical dominance. These developmental characteristics are accompanied by changes in carbohydrate metabolism and response to gibberellic acid, and a differential balance between abscisic acid, gibberellic acid, cytokinins, and auxin. Overexpression of StPP2Ac2b alters the source-sink balance, increasing the source capacity of the tuber, and the sink strength of the sprout to support its accelerated growth.

Expression of the Arabidopsis ABF4 gene in potato increases tuber yield, improves tuber quality and enhances salt and drought tolerance.

KEY MESSAGE: In this study we show that expression of the Arabidopsis ABF4 gene in potato increases tuber yield under normal and abiotic stress conditions, improves storage capability and processing quality of the tubers, and enhances salt and drought tolerance. Potato is the third most important food crop in the world. Potato plants are susceptible to salinity and drought, which negatively affect crop yield, tuber quality and market value. The development of new varieties with higher yields and increased tolerance to adverse environmental conditions is a main objective in potato breeding. In addition, tubers suffer from undesirable sprouting during storage that leads to major quality losses; therefore, the control of tuber sprouting is of considerable economic importance. ABF (ABRE-binding factor) proteins are bZIP transcription factors that regulate abscisic acid signaling during abiotic stress. ABF proteins also play an important role in the tuberization induction. We developed transgenic potato plants constitutively expressing the Arabidopsis ABF4 gene (35S::ABF4). In this study, we evaluated the performance of 35S::ABF4 plants grown in soil, determining different parameters related to tuber yield, tuber quality (carbohydrates content and sprouting behavior) and tolerance to salt and drought stress. Besides enhancing salt stress and drought tolerance, constitutive expression of ABF4 increases tuber yield under normal and stress conditions, enhances storage capability and improves the processing quality of the tubers.

Inhibition of serum-stimulated mitogen activated protein kinase by 1alpha,25(OH)2-vitamin D3 in MCF-7 breast cancer cells.

1alpha,25-Dihydroxyvitamin D3 [1alpha,25(OH)2D3], the hormonally active form of vitamin D3, has been shown to be a potent negative growth regulator of breast cancer cells both in vitro and in vivo. 1alpha,25(OH)2D3 acts through two different mechanisms. In addition to regulating gene transcription via its specific intracellular receptor (vitamin D receptor, VDR), 1alpha,25(OH)2D3 induces rapid, non-transcriptional responses involving activation of transmembrane signal transduction pathways, like growth factors and peptide hormones. The mechanisms that mediate the antiproliferative effects of 1alpha,25(OH)2D3 in breast cancer cells are not fully understood. Particularly, there is no information about the early non-genomic signal transduction effectors modulated by the hormone. The present study shows that 1alpha,25(OH)2D3 rapidly inhibits serum induced activation of ERK-1 and ERK-2 MAP kinases. The tyrosine kinase Src is involved in the pathway leading to activation of ERK 1/2 by serum. Furthermore, 1alpha,25(OH)2D3 increases the tyrosine-phosphorylated state of Src and inhibits its kinase activity, while induces the association of the VDR with Src, either in the presence or absence of serum. In parallel, the hormone rapidly increases the amounts of VDR associated to plasma membranes (PM). Pretreatment with the tyrosine phosphatase inhibitors orthovanadate or bpV (phen) prevented mitogen-activated protein kinase (MAPK) inhibition by 1alpha,25(OH)2D3. These data altogether suggest that 1alpha,25(OH)2D3 inhibits the MAPK cascade by inactivating Src tyrosine kinase through a mechanism mediated by the VDR and tyrosine phosphatases.

MAPK inhibition by 1alpha,25(OH)2-Vitamin D3 in breast cancer cells. Evidence on the participation of the VDR and Src.

1alpha,25-Dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)], the hormonally active form of Vitamin D(3), has been shown to be a potent negative growth regulator of breast cancer cells both in vitro and in vivo. 1alpha,25(OH)(2)D(3) acts through two different mechanisms. In addition to regulating gene transcription via its specific intracellular receptor (Vitamin D receptor, VDR), 1alpha,25(OH)(2)D(3) induces, rapid, non-transcriptional responses involving activation of transmembrane signal transduction pathways. The mechanisms that mediate the antiproliferative effects of 1alpha,25(OH)(2)D(3) in breast cancer cells are not fully understood. Particularly, there is no information about the early non-genomic signal transduction effectors modulated by the hormone. The present study shows that 1alpha,25(OH)(2)D(3) rapidly inhibits serum induced activation of ERK-1 and ERK-2 MAP kinases. The non-receptor tyrosine kinase Src is involved in the pathway leading to activation of ERK 1/2 by serum. Furthermore, 1alpha,25(OH)(2)D(3) increases the tyrosine-phosphorylated state of Src as well as it inhibits its kinase activity and induces the association of the VDR with Src. These data suggest that 1alpha,25(OH)(2)D(3) inhibits MAPK by inactivating Src tyrosine kinase through a so far unknown mechanism that seems to be mediated by the VDR.