AUTHOR=Xie Bin , Chen Yanhui , Zhang Yanzhen , An Xiuhong , Li Xin , Yang An , Kang Guodong , Zhou Jiangtao , Cheng Cungang 

TITLE=Comparative physiological, metabolomic, and transcriptomic analyses reveal mechanisms of apple dwarfing rootstock root morphogenesis under nitrogen and/or phosphorus deficient conditions

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1120777

DOI=10.3389/fpls.2023.1120777

ISSN=1664-462X

ABSTRACT=<p>Nitrogen (N) and phosphorus (P) are essential phytomacronutrients, and deficiencies in these two elements limit growth and yield in apple (<italic>Malus domestica</italic> Borkh.). The rootstock plays a key role in the nutrient uptake and environmental adaptation of apple. The objective of this study was to investigate the effects of N and/or P deficiency on hydroponically-grown dwarfing rootstock ‘M9-T337’ seedlings, particularly the roots, by performing an integrated physiological, transcriptomics-, and metabolomics-based analyses. Compared to N and P sufficiency, N and/or P deficiency inhibited aboveground growth, increased the partitioning of total N and total P in roots, enhanced the total number of tips, length, volume, and surface area of roots, and improved the root-to-shoot ratio. P and/or N deficiency inhibited <inline-formula><mml:math display="inline" id="im42" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mn>3</mml:mn><mml:mrow><mml:mtext> </mml:mtext><mml:mo>−</mml:mo></mml:mrow></mml:msubsup></mml:mrow></mml:math></inline-formula> influx into roots, and H<sup>+</sup> pumps played a important role in the response to P and/or N deficiency. Conjoint analysis of differentially expressed genes and differentially accumulated metabolites in roots revealed that N and/or P deficiency altered the biosynthesis of cell wall components such as cellulose, hemicellulose, lignin, and pectin. The expression of <italic>MdEXPA4</italic> and <italic>MdEXLB1</italic>, two cell wall expansin genes, were shown to be induced by N and/or P deficiency. Overexpression of <italic>MdEXPA4</italic> enhanced root development and improved tolerance to N and/or P deficiency in transgenic <italic>Arabidopsis thaliana</italic> plants. In addition, overexpression of <italic>MdEXLB1</italic> in transgenic <italic>Solanum lycopersicum</italic> seedlings increased the root surface area and promoted acquisition of N and P, thereby facilitating plant growth and adaptation to N and/or P deficiency. Collectively, these results provided a reference for improving root architecture in dwarfing rootstock and furthering our understanding of integration between N and P signaling pathways.</p>