Enhanced Autophagic Activity Improved the Root Growth and Nitrogen Utilization Ability of Apple Plants under Nitrogen Starvation.

Liuqing Huo,Xin Jia,Zijian Guo,Ping Wang,Cuiying Li,Xiaoqing Gong,Qi Wang,Li Cheng,Fengwang Ma

doi:10.3390/ijms22158085

Abstract

Autophagy is a conserved degradation pathway for recycling damaged organelles and aberrant proteins, and its important roles in plant adaptation to nutrient starvation have been generally reported. Previous studies found that overexpression of autophagy-related (ATG) gene MdATG10 enhanced the autophagic activity in apple roots and promoted their salt tolerance. The MdATG10 expression was induced by nitrogen depletion condition in both leaves and roots of apple plants. This study aimed to investigate the differences in the growth and physiological status between wild type and MdATG10-overexpressing apple plants in response to nitrogen starvation. A hydroponic system containing different nitrogen levels was used. The study found that the reduction in growth and nitrogen concentrations in different tissues caused by nitrogen starvation was relieved by MdATG10 overexpression. Further studies demonstrated the increased root growth and the higher nitrogen absorption and assimilation ability of transgenic plants. These characteristics contributed to the increased uptake of limited nitrogen nutrients by transgenic plants, which also reduced the starvation damage to the chloroplasts. Therefore, the MdATG10-overexpressing apple plants could maintain higher photosynthetic ability and possess better growth under nitrogen starvation stress.

Highlights

Nitrogen (N) is a fundamental macronutrient for plant growth and development because it is a key component of many cellular constituents, including nucleic acids, amino acids, proteins, cell walls, membranes, chlorophyll, and phytohormones [1,2]
As the present study found that the MdATG10 expression could be induced by low levels of nitrogen in both the leaves and roots of apple plants, here, we employed the transgenic and wild type (WT) apple plants to investigate the effect of autophagy on the overall physiological and growth state of apple plants under nitrogen starvation
These results suggested that the adverse effect of nitrogen deficiency on the growth of apple plants was effectively relieved by MdATG10 overexpression

Summary

Introduction

Nitrogen (N) is a fundamental macronutrient for plant growth and development because it is a key component of many cellular constituents, including nucleic acids, amino acids, proteins, cell walls, membranes, chlorophyll, and phytohormones [1,2]. Nitrogen deficiency impedes plant growth, reduces photosynthesis, hydrolyzes cell proteins, promotes plant senescence, and decreases plant productivity [3,4]. Serving as a nitrogen storage unit, more than 70% of nitrogen in plants is stored in chloroplasts under normal conditions [10]. It is this large amount of nitrogen requirement to construct the photosynthetic system that results in the need for nitrogenous fertilizer. As leaves are the main organ for performing photosynthesis in plants, chlorophyll degradation and the leaf senescence phenotype lead to decreased photosynthetic capacity of plants [13]

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