Mitogen-activated protein (MAP) kinase signaling pathways are major regulators o
ID: 261180 • Letter: M
Question
Mitogen-activated protein (MAP) kinase signaling pathways are major regulators of proliferation, differentiation, and stress effectors. The core of the MAP kinase signal transduction cascade is composed of a three-kinase module consisting of a MAP kinase kinase kinase, a MAP kinase kinase (or MEK), and a MAP kinase, that are sequentially activated after cellular stimulation [1]. Upon pathway stimulation, MAP kinases may translocate to the nucleus where they can control the activation of gene transcription through the phosphorylation of transcription factors [2], or they can target other protein kinases or membrane and cytosolic proteins [3]. Although this module appears to be conserved in all eukaryotes, novel combinations of molecules associated with the module may have arisen throughout evolution that govern processes that are particular to the lifestyle and morphological requirements of different organisms. The MAP kinases p45Ntf4 and SIPK are expressed in tobacco pollen grains and both are activated upon rehydration of the tobacco pollen [4,5]. In planta the mature pollen grain is dehydrated and is essentially in a quiescent state. When a pollen grain lands on a stigma it rapidly rehydrates, leading to cell swelling, reorganization of the cytoskeleton, and the emergence of a pollen tube that transports the sperm cells to the ovary [6]. The reorganization of the cytoskeleton involves the polymerization and re-orientation of actin filaments at the pore where the pollen tube eventually emerges, and the extension of actin cables along the growing pollen tube [7]. A number of actin-remodeling proteins are expressed in pollen, such as the actin-binding protein profilin [8,9], and actin-depolymerizing factors (ADF) and ADF-modulating proteins such as AIP1 [10]. Thepollen-specific expression of a subset of these gene families indicates the presence of a particular regulatory process in pollen that controls actin turnover. Profilin is an actin monomer-binding protein thatregulates the polymerization of actin filaments [11]. Apart from actin, profilin can also bind phosphoinositides and proline-rich proteins [12]. These features of profilin suggest that it may provide a link between signal transduction pathways and changes in cellular architecture [13], and profilin can be phosphorylated by protein kinase C [14]. A role for profilin in signaling in pollen has been proposed [15]. Actin polymerization is essential for pollen tube growth and profilin appears to be involved in this process [16]. Given that actin reorganization occurs upon pollen germination [7], that profilin is highly expressed in mature pollen grains [8,17,18], and that MAP kinases are rapidly activated after pollen hydration [4,5], we investigated if a link could exist between these elements by testing whether profilin might be a MAP kinase substrate.
Based on the above text , answer the folowing:
1. State 3 specific background facts found in the introduction.
2. What do the authors suggest is the major accomplishment(s) of the manuscript?
Explanation / Answer
1. The 3 specific background facts that had been found in the introduction are:
2. According to the authors, the major accomplishments of the manuscript are: recognition of the role of profilin in signaling of pollen, and that profilin is found in the mature grains of pollen and after pollen hydration occurs, there would be activation of the MAP kinases.