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Several nucleoporins in the nuclear pore complex (NPC) have been reported to be involved in abiotic stress responses in plants. However, the molecular mechanism of how NPC regulates abiotic stress responses, especially the expression of stress responsive genes remains poorly understood. From a forward genetics screen using an abiotic stress-responsive luciferase reporter (RD29A-LUC) in the sickle-1 (sic-1) mutant background, we identified a suppressor caused by a mutation in NUCLEOPORIN 85 (NUP85), which exhibited reduced expression of RD29A-LUC in response to ABA and salt stress. Consistently, the ABA and salinity induced expression of several stress responsive genes such as RD29A, COR15A and COR47 was significantly compromised in nup85 mutants and other nucleoporin mutants such as nup160 and hos1. Subsequently, Immunoprecipitation and mass spectrometry analysis revealed that NUP85 is potentially associated with HOS1 and other nucleoporins within the nup107-160 complex, along with several mediator subunits. We further showed that there is a direct physical interaction between MED18 and NUP85. Similar to NUP85 mutations, MED18 mutation was also found to attenuate expression of stress responsive genes. Taken together, we not only revealed the involvement of NUP85 and other nucleoporins in regulating ABA and salt stress responses, but also uncovered a potential relation between NPC and mediator complex in modulating the gene expression in plants. [ABSTRACT FROM AUTHOR]

Arabidopsis hypersensitive-induced reaction (At HIR) proteins function in plant innate immunity. However, the underlying mechanisms by which At HIRs participate in plant immunity remain elusive. Here, using VA- TIRFM and FLIM- FRET, we revealed that At HIR1 is present in membrane microdomains and co-localizes with the membrane microdomain marker REM1.3. Single-particle tracking analysis revealed that membrane microdomains and the cytoskeleton, especially microtubules, restrict the lateral mobility of At HIR1 at the plasma membrane and facilitate its oligomerization. Furthermore, protein proximity index measurements, fluorescence cross-correlation spectroscopy, and biochemical experiments demonstrated that the formation of the At HIR1 complex upon pathogen perception requires intact microdomains and cytoskeleton. Taken together, these findings suggest that microdomains and the cytoskeleton constrain At HIR1 dynamics, promote At HIR1 oligomerization, and increase the efficiency of the interactions of At HIR1 with components of the At HIR1 complex in response to pathogens, thus providing valuable insight into the mechanisms of defense-related responses in plants. [ABSTRACT FROM AUTHOR]

CLAVATA1 ( CLV1) is a receptor protein expressed in the shoot apical meristem ( SAM) that translates perception of a non-cell-autonomous CLAVATA3 ( CLV3) peptide signal into altered stem cell fate. CLV3 reduces expression of WUSCHEL ( WUS) and FANTASTIC FOUR 2 ( FAF2) in the SAM. Expression of WUS and FAF2 leads to maintenance of undifferentiated stem cells in the SAM. CLV3 binding to CLV1 inhibits expression of these genes and controls stem cell fate in the SAM through an unidentified signaling pathway. Cytosolic Ca2+ elevations, cyclic nucleotide ( cGMP)-activated Ca2+ channels, and cGMP have been linked to signaling downstream of receptors similar to CLV1. Hence, we hypothesized that cytosolic Ca2+ elevation mediates the CLV3 ligand/ CLV1 receptor signaling that controls meristem stem cell fate. CLV3 application to Arabidopsis seedlings results in elevation of cytosolic Ca2+ and cGMP. CLV3 control of WUS was prevented in a genotype lacking a functional cGMP-activated Ca2+ channel. In wild-type plants, CLV3 inhibition of WUS and FAF2 expression was impaired by treatment with either a Ca2+ channel blocker or a guanylyl cyclase inhibitor. When CLV3-dependent repression of WUS is blocked, altered control of stem cell fate leads to an increase in SAM size; we observed a larger SAM size in seedlings treated with the Ca2+ channel blocker. These results suggest that the CLV3 ligand/ CLV1 receptor system initiates a signaling cascade that elevates cytosolic Ca2+, and that this cytosolic secondary messenger is involved in the signal transduction cascade linking CLV3/ CLV1 to control of gene expression and stem cell fate in the SAM. [ABSTRACT FROM AUTHOR]