Plant lectins: the ties that bind in root symbiosis and plant defense

Lectins are a diverse group of carbohydrate-binding proteins that are found within and associated with organisms from all kingdoms of life. Several different classes of plant lectins serve a diverse array of functions. The most prominent of these include participation in plant defense against predators and pathogens and involvement in symbiotic interactions between host plants and symbiotic microbes, including mycorrhizal fungi and nitrogen-fixing rhizobia. Extensive biological, biochemical, and molecular studies have shed light on the functions of plant lectins, and a plethora of uncharacterized lectin genes are being revealed at the genomic scale, suggesting unexplored and novel diversity in plant lectin structure and function. Integration of the results from these different types of research is beginning to yield a more detailed understanding of the function of lectins in symbiosis, defense, and plant biology in general

Heat stress activates phospholipase D and triggers PIP2 accumulation at the plasma membrane and nucleus

Heat stress induces an array of physiological adjustments that facilitate continued homeostasis and survival during periods of elevated temperatures. Here, we report that within minutes of a sudden temperature increase, plants deploy specific phospholipids to specific intracellular locations: phospholipase D (PLD) and a phosphatidylinositolphosphate kinase (PIPK) are activated, and phosphatidic acid (PA) and phosphatidylinositol 4,5-bisphosphate (PIP2) rapidly accumulate, with the heat-induced PIP2 localized to the plasma membrane, nuclear envelope, nucleolus and punctate cytoplasmic structures. Increases in the steady-state levels of PA and PIP2 occur within several minutes of temperature increases from ambient levels of 20-25°C to 35°C and above. Similar patterns were observed in heat-stressed Arabidopsis seedlings and rice leaves. The PA that accumulates in response to temperature increases results in large part from the activation of PLD rather than the sequential action of phospholipase C and diacylglycerol kinase, the alternative pathway used to produce this lipid. Pulse-labelling analysis revealed that the PIP2 response is due to the activation of a PIPK rather than inhibition of a lipase or a PIP2 phosphatase. Inhibitor experiments suggest that the PIP2 response requires signalling through a G-protein, as aluminium fluoride blocks heat-induced PIP2 increases. These results are discussed in the context of the diverse cellular roles played by PIP2 and PA, including regulation of ion channels and the cytoskeleton