Chloride (Clˉ) and nitrate (NO₃ˉ) are the most abundant inorganic anions in plants, sharing physical properties in solution and showing strong dynamic interactions. Thus, a higher tissue concentration of Clˉ leads to a lower concentration of NO₃ˉ and vice versa. This has been explained by the fact that both anions share and compete for similar transport mechanisms, meaning that Clˉ reduces the plants ability to take up NO₃ˉ from the soil. For this reason, Clˉ has been traditionally considered harmful to agriculture. Since NO₃ˉ is an essential nitrogen source, it is currently considered that plants strongly prioritize the uptake of NO₃ˉ over that of Clˉ. NO₃ˉ preference has been explained as: i) the occurrence of NO₃ˉ -selective transporters (e.g. AtNPF6.3 and MtNPF6.7) that mediate Clˉ only when NO₃ˉ is not available (Wen et al., 2018; Xiao et al., 2021); and ii) the occurrence of a signaling mechanism activated by NOзˉ supply that induces selective NO₃ˉ transporters (e.g. MtNPF6.7) while represses selective Clˉ transporters (e.g. MtNPF6.5; Xiao et al., 2021). The signaling cascade involves the AtNPF6.3 transceptor (transporter + receptor), the calcium transporter AtCNGC15 and the transcription factor AtNLP7. We have recently shown that Clˉ has a reduced impact on NO₃ˉ transport while signifcantly improving NO₃ˉ utilization and nitrogen-use efciency (NUE) in several plant species (Rosales et al., 2020). We hypothesize that regulation of NO₃ˉ and Clˉ homeostasis is more complex than currently believed, and other transporters diferent to those of the NPF6 subclade are involved in Clˉ uptake. To better understand the regulation of Clˉ uptake in plants and its interaction with NO₃ˉ availability, Clˉ accumulation has been quantifed in Arabidopsis mutant lines with lack of function for a number of relevant NO₃ˉ transport and NO₃ˉ signaling proteins. References • Rosales et al (2020). Front Plant Sci 11(442) • Wen et al (2018). Front Plant Sci 9(973) • Xiao et al (2021) EMBO J 40:e106847.

We acknowledge funding by MICINN-FEDER Projects PID2021-125157OB-I00 and RTI2018-094460-B-100, and the CSIC-2021-JAE-INTRO-21 fellowship.

Poster presentado en el XVI Meeting of Plant Molecular Biology (RPMB) 14-16 sept. 2022, Sevilla

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