Recent NMT Publications 9/26/22

A quick look at some recent NMT Publications from 2022

MYB308-mediated transcriptional activation of plasma membrane H⁺-ATPase 6 promotes iron uptake in citrus

Abstract: Iron-deficiency chlorosis is a common nutritional disorder in crops grown on alkaline or calcareous soils. Although the acclimation mechanism to iron deficiency has been investigated, the genetic regulation of iron acquisition is still unclear. Here, by comparing the iron uptake process between the iron-poor-soil-tolerant citrus species Zhique (ZQ) and the iron-poor-soil-sensitive citrus species trifoliate orange (TO), we discovered that enhanced root H ⁺ efflux is crucial for the tolerance to iron deficiency in ZQ. The H⁺ efflux is mainly regulated by a plasma membrane-localized H⁺-ATPase, HA6, the expression of which is upregulated in plants grown in soil with low iron content, and significantly higher in the roots of ZQ than TO. Overexpression of the HA6 gene in the Arabidopsis thaliana aha2 mutant, defective in iron uptake, recovered the wild-type phenotype. In parallel, overexpression of the HA6 gene in TO significantly increased iron content of plants. Moreover, an iron deficiency-induced transcription factor, MYB308, was revealed to bind the promoter and activate the expression of HA6 in ZQ in yeast one-hybrid, electrophoretic mobility shift, and dual-luciferase assays. Overexpression of MYB308 in ZQ roots significantly increased the expression level of the HA6 gene. However, MYB308 cannot bind or activate the HA6 promoter in TO due to the sequence variation of the corresponding MYB308 binding motif. Taking these results together, we propose that the MYB308 could activate HA6 to promote root H⁺ efflux and iron uptake, and that the distinctive MYB308-HA6 transcriptional module may be, at least in part, responsible for the iron deficiency tolerance in citrus.

Fan Zhengyan, Wu Yifang, Zhao Liuying, Fu Lina, Deng Lile, Deng Jiarui, Ding Dekuan, Xiao Shunyuan, Deng Xiuxin, Peng Shuang, Pan Zhiyong. MYB308-mediated transcriptional activation of plasma membrane H+-ATPase 6 promotes iron uptake in citrus. Horticulture Research. 2022;, uhac088, doi.org/10.1093/hr/uhac088

Characteristics of NH₄⁺ and NO₃^- Fluxes in Taxodium Roots under Different Nitrogen Treatments

Abstract: To understand the characteristics of net NH₄⁺ and NO₃^- fluxes and their relation with net H⁺ fluxes in Taxodium, net fluxes of NH₄⁺, NO₃^- and H⁺ were detected by a scanning ion-selective electrode technique under different forms of fixed nitrogen (N) and experimental conditions. The results showed that higher net NH₄⁺ and NO₃^- fluxes occurred at 2.1-3.0 mm from the root apex in T.ascendens and T. distichum. Compared to NH₄⁺ or NO₃^- alone, more stable net NH₄⁺ and NO₃^- fluxes were found under NH₄NO₃ supply conditions, of which net NH₄⁺ flux was promoted at least 1.71 times by NO₃^-, whereas net NO₃^- flux was reduced more than 81.66% by NH₄⁺ in all plants, which indicated that NH₄⁺ is preferred by Taxodium plants. T. ascendens and T. mucronatum had the largest net NH₄⁺ and total N influxes when NH₄⁺:NO₃^- was 3:1. ¹⁵N Atom% and activities of N assimilation enzymes were improved by single N fertilization in the roots of T. distichum. In most cases, net H⁺ fluxes were tightly correlated with net NH₄⁺ and NO₃^- fluxes. Thus, both N forms and proportions could affect N uptake of Taxodium. These findings could provide useful guidance for N management for better productivity of Taxodium plants.

Wu S, Hua J, Lu Y, Zhang R, Yin Y. Characteristics of NH₄⁺ and NO₃^- Fluxes in Taxodium Roots under Different Nitrogen Treatments. Plants (Basel). 2022 Mar 28;11(7):894. doi: 10.3390/plants11070894. PMID: 35406875; PMCID: PMC9003431.

Nitrate transporter NRT1.1 and anion channel SLAH3 form a functional unit to regulate nitrate-dependent alleviation of ammonium toxicity

Abstract: Ammonium (NH₄⁺ ) and nitrate (NO₃^- ) are major inorganic nitrogen (N) sources for plants. When serving as the sole or dominant N supply, NH₄⁺ often causes root inhibition and shoot chlorosis in plants, known as ammonium toxicity. NO₃^- usually causes no toxicity and can mitigate ammonium toxicity even at low concentrations, referred to as nitrate-dependent alleviation of ammonium toxicity. Our previous studies indicated a NO₃^- efflux channel SLAH3 is involved in this process. However, whether additional components contribute to NO₃^- -mediated NH₄⁺ detoxification is unknown. Previously, mutations in NO₃^- transporter NRT1.1 were shown to cause enhanced resistance to high concentrations of NH₄⁺ . Whereas, in this study, we found when the high-NH₄⁺ medium was supplemented with low concentrations of NO₃^- , nrt1.1 mutant plants showed hyper-sensitive phenotype instead. Furthermore, mutation in NRT1.1 caused enhanced medium acidification under high-NH₄⁺ /low-NO₃^- condition, suggesting NRT1.1 regulates ammonium toxicity by facilitating H⁺ uptake. Moreover, NRT1.1 was shown to interact with SLAH3 to form a transporter-channel complex. Interestingly, SLAH3 appeared to affect NO₃^- influx while NRT1.1 influenced NO₃^- efflux, suggesting NRT1.1 and SLAH3 regulate each other at protein and/or gene expression levels. Our study thus revealed NRT1.1 and SLAH3 form a functional unit to regulate nitrate-dependent alleviation of ammonium toxicity through regulating NO₃^- transport and balancing rhizosphere acidification.

Xiao C, Sun D, Liu B, Fang X, Li P, Jiang Y, He M, Li J, Luan S, He K. Nitrate transporter NRT1.1 and anion channel SLAH3 form a functional unit to regulate nitrate-dependent alleviation of ammonium toxicity. J Integr Plant Biol. 2022 Mar 1. doi: 10.1111/jipb.13239. Epub ahead of print. PMID: 35229477.