VviAMT4;1 Is a High-Affinity Ammonium Transporter in Table Grape.

Area of Science:

• Plant Physiology
• Molecular Biology
• Biochemistry

Background:

• Ammonium transporters (AMTs) are vital membrane proteins for ammonium (NH4+ or NH3) uptake and transport.
• Understanding plant nitrogen assimilation mechanisms is crucial for agricultural productivity.

Purpose of the Study:

• To isolate and characterize the ammonium transporter-encoding gene VviAMT4;1 from table grape 'Yanpu No.2'.
• To investigate the expression patterns and functional properties of VviAMT4;1 in response to nutrient availability and environmental conditions.

Main Methods:

• Gene isolation and identification of VviAMT4;1 from table grape.
• Quantitative analysis of VviAMT4;1 gene expression across different tissues and under varying ammonium concentrations.
• Functional complementation of yeast mutants to assess transporter activity.
• 15N isotope-labeled uptake kinetics to determine kinetic parameters (Km, Vmax).

Main Results:

• VviAMT4;1 expression was highest in grape roots and significantly upregulated under ammonium depletion.
• Yeast complementation confirmed VviAMT4;1's function as a high-affinity ammonium transporter (Km = 49.58 ± 4.66 μmol·L-1).
• VviAMT4;1 demonstrated weak uptake of methylamine and potential feedback inhibition by internal ammonium.

Conclusions:

• VviAMT4;1 plays a significant role in ammonium uptake and transport in table grapes, particularly in root tissues.
• The transporter exhibits high affinity for ammonium and is responsive to nitrogen availability.
• Findings contribute to understanding nitrogen transport mechanisms in fruit trees, with implications for crop improvement.