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domains protrude in to the cytosol (214). Related to these in mammals and yeasts, plant CYB5s also usually serve as vital electron shuttle intermediates for biosynthetic reactions, for instance lipid, steroid, and lignin biosynthesis (247). CYB5 proteins physically associate with AtRTE1 and AtSUT4 to mediate the ethylene response and sucrose transport, respectively (280). Here, we located that the ER-localized OsCYB52 protein interacts with OsHAK21. Our biochemical analyses indicated that the OsCYB5-2 sHAK21 interaction enhances the apparent affinity of OsHAK21 for K+-binding and improves K+ transport activity. We deliver additional genetic evidenceoil salinity is a major limiting element for plant development and crop production. Salinity tolerance in plants is conferred by sustaining an optimal cytosolic potassium/sodium (K+/Na+) ratio as opposed to the absolute Na+ concentration (1, 2). For the duration of salt pressure, high-Na+ levels disrupt K+/Na+ homeostasis by reducing K+ uptake and growing K+ efflux (3, four). Rising K+ uptake from high-Na+ environments can proficiently enhance plant salt tolerance by preserving K+/Na+ homeostasis (five). The absorption of K+ in roots and also the distribution of K+ all through the plant are mainly regulated by K+ channels and transporters (9). The K+ transporter/high-affinity K+ transporter/K+ uptake protein (KT/HAK/KUP) family members is one of the principal K+ acquisition systems in plants (10). They are involved in processes like K+ uptake from the soil, K+ translocation, water movement regulation, and developmental processes (11, 12). Kinetic analyses of plant roots of Rb+ (as a K+ tracer) involving comparison of wild-type (WT) and AtHAK5 knockout mutant have revealed that AtHAK5 functions in K+ deprivation nduced, high-affinity K+ uptake in Arabidopsis roots (13, 14). In monocot rice, some HAKs, which include OsHAK1, OsHAK5, OsHAK16, and OsHAK21, play critical roles in precise tissues and/or cells when plants are subjected to salt anxiety (eight, 158). One example is, OsHAK21 transcription is strongly up-regulated in roots following salt stress, and knockdown of this gene leads to less K+ and more Na+ accumulation in plants. In addition, OsHAK21 expression is usually valuable for anPNAS 2021 Vol. 118 No. 50 eSSignificanceHigh-affinity K+ (HAK) transporter-P2X3 Receptor Purity & Documentation mediated K+ uptake has an essential role when plants are subjected to stresses. This work identifies a mechanism of HAK regulation. The affinity of HAK at the plasma membrane for K+ depends on the binding of a cytochrome (CYB5) protein at the endoplasmic reticulum. This improves K+ uptake as well as the capacity of plants to survive under STAT6 web saline conditions. The HAK YB5 interaction not only constitutes a mechanism of HAK regulation but in addition reflects interorganelle communication mediated by functional protein interactions under situations of pressure.Author contributions: T.S., W.L., and W.Z. designed investigation; T.S., Y. Shi, L.S., C.C., Y. Shen, W.J., Q.T., and W.L. performed research; T.S., Y. Shi, L.S., C.C., Y. Shen, W.J., Q.T., and W.L. analyzed information; T.S., F.L., W.L., and W.Z. wrote the paper; and F.L. and W.Z. supervised the research. The authors declare no competing interest. This short article is a PNAS Direct Submission. This open access post is distributed under Creative Commons AttributionNonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).1 To whom correspondence may very well be addressed. Email: liwenyu0708@163 or [email protected] short article consists of supporting data on the net at http: