Toll-like receptors transduce their signals through the adaptor molecule MyD88 and members of the IL-1R-associated kinase family (IRAK-1, 2, M and 4). IRAK-1 and IRAK-2, known to form Myddosomes with MyD88-IRAK-4, mediate TLR7-induced TAK1-dependent NFjB activation. IRAK-M was previously known to function as a negative regulator that prevents the dissociation of IRAKs from MyD88, thereby inhibiting downstream signalling. However, we now found that IRAK-M was also able to interact with MyD88-IRAK-4 to form IRAK-M Myddosome to mediate TLR7-induced MEKK3-dependent second wave NFjB activation, which is uncoupled from post-transcriptional regulation. As a result, the IRAK-M-dependent pathway only induced expression of genes that are not regulated at the post-transcriptional levels (including inhibitory molecules SOCS1, SHIP1, A20 and IjBa), exerting an overall inhibitory effect on inflammatory response. On the other hand, through interaction with IRAK-2, IRAK-M inhibited TLR7-mediated production of cytokines and chemokines at translational levels. Taken together, IRAK-M mediates TLR7-induced MEKK3-dependent second wave NFjB activation to produce inhibitory molecules as a negative feedback for the pathway, while exerting inhibitory effect on translational control of cytokines and chemokines.

Plasma membrane intrinsic proteins (PIPs) are a subfamily of aquaporins that enable fast and controlled translocation of water across the membrane. In this study, we systematically identified and cloned ten PIP genes from rice. Based on the similarity of the amino acid sequences they encoded, these rice PIP genes were classified into two groups and designated as OsPIP1-1 to OsPIP1-3 and OsPIP2-1 to OsPIP2-7 following the nomenclature of PIP genes in maize. Quantitative RT-PCR analysis identified three root-specific and one leaf-specific OsPIP genes. Furthermore, the expression profile of each OsPIP gene in response to salt, drought and ABA treatment was examined in detail. Analysis on transgenic plants over-expressing of either OsPIP1 (OsPIP1-1) or OsPIP2 (OsPIP2-2) in wild-type Arabidopsis, showed enhanced tolerance to salt (100 mM of NaCl) and drought (200 mM of mannitol), but not to salt treatment of higher concentration (150 mM of NaCl). Taken together, these data suggest a distinct role of each OsPIP gene in response to different stresses, and should add a new layer to the understanding of the physiological function of rice PIP genes.

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