Cantero A, Barthakur S, Bushart TJ, Chou S, Morgan RO, Fernandez MP, Clark GB, Roux SJ.
Expression profiling of the Arabidopsis annexin gene family during germination, de-etiolation and abiotic stress. Plant Physiol Biochem. 44 (1) :13-24.
AbstractAnnexins are a multigene family in most plant species and are suggested to play a role in a wide variety of essential cellular processes. In Arabidopsis thaliana there are eight different annexins (AnnAt1-8), which range from 29% to 83% in deduced amino acid sequence identity. As a first step toward clarifying the individual functions of these annexins, in this study we have used quantitative real time reverse transcription PCR to assess their differential expression in different tissues or after different stimuli. We determined which annexins are expressed during germination and early seedling growth by assaying annexin expression levels in dry and germinating seeds and in 7-day-old light-grown seedlings. Our results indicate that transcripts for all eight annexins are present in germinating seeds and that transcript levels for all the annexins increase by 7 days of normal growth. We assayed transcript levels in dark grown roots, cotyledons, and hypocotyls and found that the relative abundance of each annexin varied in these dark-grown tissues. We also examined the effects of red and far red light treatments on annexin expression in 5.5-day-old etiolated seedlings. Light treatments significantly altered transcript levels in hypocotyls and cotyledons for only two members of the gene family. Finally, we monitored annexin expression changes in response to a variety of abiotic stresses. We found that the expression of most of the Arabidopsis annexin genes is differentially regulated by exposure to salt, drought, and high- and low-temperature conditions, indicating a likely role for members of this gene family in stress responses.
Jeter CR, Roux SJ.
Plant responses to extracellular nucleotides: Cellular processes and biological effects. Purinergic Signal. 2 (3) :443-9.
AbstractHigher plants exhibit cellular responsiveness to the exogenous application of purine nucleotides in a manner consistent with a cell-cell signaling function for these molecules. Like animals, plants respond to extracellular ATP, ADP, and stable analogues (e.g., ATPgammaS and ADPbetaS) by increasing the cytoplasmic concentration of calcium. Agonist substrate specificity and concentration dependency suggest receptor mediation of these events, and, although the identity of the plant receptor is currently unknown, pharmacological analysis points to the involvement of a plasma membrane-localized calcium channel. Extracellular ATP can also induce the production of reactive oxygen species and stimulate an increase in the mRNA levels of a number of stress- and calcium-regulated genes, suggesting a role for nucleotide-based signaling in plant wound and defense responses. Furthermore, the growth and development of plants can also be altered by the application of external ATP. Recent studies are only beginning to uncover the complexities of plant signaling networks activated in response to extracellular ATP and how these might interact to affect plant physiological processes.
Song CJ, Steinebrunner I, Wang X, Stout SC, Roux SJ.
Extracellular ATP induces the accumulation of superoxide via NADPH oxidases in Arabidopsis. Plant Physiol. 140 (4) :1222-32.
AbstractExtracellular ATP can serve as a signaling agent in animal cells, and, as suggested by recent reports, may also do so in plant cells. In animal cells it induces the production of reactive oxygen species through the mediation of NADPH oxidase. Similarly, here we report that in leaves of Arabidopsis (Arabidopsis thaliana), applied ATP, but not AMP or phosphate, induces the accumulation of superoxide (O2-) in a biphasic, dose-dependent manner, with a threshold at 500 nm ATP. This effect did not require ATP hydrolysis for it was mimicked by ATPgammaS. ATP also induced increased levels of Arabidopsis respiratory burst oxidase homolog D (AtrbohD) mRNA, but ATP-treated plants that had disrupted AtrbohD and AtrbohF genes did not accumulate O2-, indicating that NADPH oxidases are responsible for the induced O2- accumulation. Inhibitors of mammalian P2-type ATP receptors abolished ATP-induced O2- production, suggesting that the ATP effects may be mediated through P2-like receptors in plants. Cytosolic Ca2+ and calmodulin are likely to help transduce the ATP responses, as they do in animal cells, because a Ca2+ channel blocker, a Ca2+ chelator, and calmodulin antagonist all reduced ATP-induced O2- accumulation. Furthermore, ATP treatment enhanced the expression of genes that are induced by wounds and other stresses. The ATP measured at wound sites averaged 40 microm, well above the level needed to induce O2- accumulation and gene expression changes. Transgenic plants overexpressing an apyrase gene had reduced O2- production in response to applied ATP and wounding. Together, these data suggest a possible role for extracellular ATP as a signal potentially in wound and stress responses.