Abstract
Nitrogen is an essential element for plant growth and yield. Improving Nitrogen Use Efficiency (NUE) of crops could potentially reduce the application of chemical fertilizer and alleviate environmental damage. To identify new NUE genes is therefore an important task in molecular breeding. Macroautophagy (autophagy) is an intracellular process in which damaged or obsolete cytoplasmic components are encapsulated in double membraned vesicles termed autophagosomes, then delivered to the vacuole for degradation and nutrient recycling. One of the core components of autophagosome formation, ATG8, has been shown to directly mediate autophagosome expansion, and the transcript of which is highly inducible upon starvation. Therefore, we postulated that certain homologs of Saccharomyces cerevisiae ATG8 (ScATG8) from crop species could have potential for NUE crop breeding. A soybean (Glycine max, cv. Zhonghuang-13) ATG8, GmATG8c, was selected from the 11 family members based on transcript analysis upon nitrogen deprivation. GmATG8c could partially complement the yeast atg8 mutant. Constitutive expression of GmATG8c in soybean callus cells not only enhanced nitrogen starvation tolerance of the cells but accelerated the growth of the calli. Transgenic Arabidopsis over-expressing GmATG8c performed better under extended nitrogen and carbon starvation conditions. Meanwhile, under optimum growth conditions, the transgenic plants grew faster, bolted earlier, produced larger primary and axillary inflorescences, eventually produced more seeds than the wild-type. In average, the yield was improved by 12.9%. We conclude that GmATG8c may serve as an excellent candidate for breeding crops with enhanced NUE and better yield.
Highlights
The vigor of plants is largely dependent on inorganic nitrogen (N), principally in the form of NO32 and NH4+, and 85–90 million tons of nitrogenous fertilizers are applied worldwide annually [1,2]
When a phylogenetic tree was built with ATG8 homologs from Arabidopsis, several major crop species including rice and maize, and lower green plants, the soybean ATG8s fall into three subgroups (Fig. 1A)
GmATG8c Enhanced Tolerance to Nitrogen Starvation in Transgenic Arabidopsis We evaluated the nitrogen use efficiency (NUE) potential of GmATG8c in the model plant Arabidopsis. 35S:GmATG8c was introduced into Arabidopsis by floral dipping
Summary
The vigor of plants is largely dependent on inorganic nitrogen (N), principally in the form of NO32 and NH4+, and 85–90 million tons of nitrogenous fertilizers are applied worldwide annually [1,2]. Breeding crops with high nitrogen use efficiency (NUE) and better yield has always been a major goal for breeders, and the identification of new potential NUE genes is important for scientists. Though capable of biological N2 fixation when associated with Rhizobia bacteria, soybean acquires a large portion (from 40% to 75%) of nitrogen from soil, depending on the inorganic nitrogen content of soil [6]. It is critical to identify useful soybean genes for the development of new transgenic soybean cultivars with high NUE and better yield
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