Abstract
Enhancing nitrogen (N) use efficiency is a potential way to reduce excessive nitrogen application and increase yield. Autophagy is a conserved degradation system in the evolution of eukaryotic cells and plays an important role in plant development and stress response. Autophagic cores have two conjugation pathways that attach the product of autophagy-related gene 8 (ATG8) to phosphatidylethanolamine (PE) and ATG5 to ATG12, respectively, which then help with vesicle elongation and enclosure. Rice has six ATG8 genes, which have not been functionally confirmed so far. We identified the rice gene OsATG8b and characterized its role in N remobilization to affect grain quality by generating transgenic plants with its over-expression and knockdown. Our study confirmed the autophagy activity of OsATG8b through the complementation of the yeast autophagy-defective mutant scatg8 and by observation of autophagosome formation in rice. The autophagy activity is higher in OsATG8b-OE lines and lower in OsATG8b-RNAi than that in wild type (ZH11). 15N pulse-chase analysis revealed that OsATG8b-OE plants conferred higher N recycling efficiency to grains, while OsATG8b-RNAi transgenic plants exhibited lower N recycling efficiency and poorer grain quality. The autophagic role of OsATG8b was experimentally confirmed, and it was concluded that OsATG8b-mediated autophagy is involved in N recycling to grains and contributes to the grain quality, indicating that OsATG8b may be a potential gene for molecular breeding and cultivation of rice.
Highlights
Nitrogen (N) is one of the most limiting nutrients for crop yield
To explore the relationship between N remobilization derived by autophagy and rice grain quality, we analyzed the expression of OsATG8s in developing endosperm by searching the Rice Expression Profile Database (RiceXpro)1 and found that only Oryza sativa autophagic-related gene 8b (OsATG8b) expression increased with endosperm development compared with OsATG8a and OsATG8c (Supplementary Figure S8)
These data indicated that the OsATG8b may be a potential rice ATG8 gene in grain filling, and it was chosen for further analyses
Summary
Increasing N utilization efficiency (NUE) is important for increasing yield and reducing production cost and for avoiding environmental pollution and keeping agriculture sustainable (Good et al, 2004; Masclaux-Daubresse et al, 2010). Plant N utilization involves complex mechanisms of absorption, translocation, assimilation, and remobilization. Of those steps, N remobilization plays an important role during seed filling (Masclaux-Daubresse et al, 2008, 2010). Most N uptake is directed to leaves, in which most proteins are synthesized. Leaf proteins degrade rapidly to amino acids and small peptides, which are transported to seeds (Masclaux-Daubresse et al, 2008). Bulk organelles and cytosolic macromolecules with low selectivity and high throughput (Suzuki and Ohsumi, 2007)
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