Abscisic Acid Acts as a Regulator of Molecular Trafficking through Plasmodesmata in the Moss Physcomitrella patens.

In multi-cellular organisms, cell-to-cell communication is crucial for adapting to changes in the surrounding environment. In plants, plasmodesmata (PD) provide a unique pathway for cell-to-cell communication. PD interconnect most cells and generate a cytoplasmic continuum, allowing the trafficking of various micro- and macromolecules between cells. This molecular trafficking through PD is dynamically regulated by altering PD permeability dependent on environmental changes, thereby leading to an appropriate response to various stresses; however, how PD permeability is dynamically regulated is still largely unknown. Moreover, studies on the regulation of PD permeability have been conducted primarily in a limited number of angiosperms. Here, we studied the regulation of PD permeability in the moss Physcomitrella patens and report that molecular trafficking through PD is rapidly and reversibly restricted by abscisic acid (ABA). Since ABA plays a key role in various stress responses in the moss, PD permeability can be controlled by ABA to adapt to surrounding environmental changes. This ABA-dependent restriction of PD trafficking correlates with a reduction in PD pore size. Furthermore, we also found that the rate of macromolecular trafficking is higher in an ABA-synthesis defective mutant, suggesting that the endogenous level of ABA is also important for PD-mediated macromolecular trafficking. Thus, our study provides compelling evidence that P. patens exploits ABA as one of the key regulators of PD function.

Theoretical method for evaluation of therapeutic effects and adverse effects of epidermal growth factor receptor tyrosine kinase inhibitors in clinical treatment.

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are used for non-small cell lung cancer patients with an EGFR gene mutation. However, skin disorders are known as adverse events. In the present study, we investigated whether EGFR-TK occupancy is useful as an index for assessing clinical efficacy and adverse events for the proper use and development of EGFR-TKIs. Average binding occupancies (Φ ss) of EGFR-TKIs, gefitinib and erlotinib, for the EGFR-TK of cancer or skin cells were calculated. The relationships of Φ ss with response rate (RR) or frequency of rash were analyzed using the ternary complex model. Then, the relationships between the dose of EGFR-TKIs and RR or frequency of rash were examined. Gefitinib showed a greater difference for Φ ss value for both wild-type and mutant EGFR as compared to erlotinib at usual dose. The RR increased in a nonlinear manner rapidly rising when Φ ss exceeded 95%. It was thought that a very high Φ ss value might be needed to obtain the therapeutic effect of EGFR-TKIs. Meanwhile, the frequency of rash increased in a linear manner along with elevation of Φ ss. It was shown that the K d ratio (K d for mutant/K d for wild type) was less than 0.001, when the high RR and low frequency of rash were obtained simultaneously. The results showed that the therapeutic effects and skin disorder can be assessed by using Φ ss. Furthermore, it is likely that a proper choice of drug and dose can be made by using Φ ss in EGFR-TKI therapy.