Leaf Senescence of Soybean at Reproductive Stage is Associated with Induction of Autophagy-Related Genes, GmATG8c, GmATG8i and GmATG4

Autophagy appears to function in bulk protein degradation and N remobilization in senescence. Depodding of soybean suppresses N remobilization from leaves, leading to "green stem syndrome". Expression of autophagy-related genes (ATGs) and N contents of the leaves and stem was analyzed in soybean plants from none (control), half (50% depodding) and all (100% depodding) of flowers and pods were removed at the reproductive 5 stage. Total N content and SPAD in leaves of the plant after 100% depodding were retained at a constant level and those after 50% depodding gradually decreased from 4 to 5 wk after depodding, while those in the control plants rapidly decreased during this period. Expression of GmATG8c and GmATG8i in leaves peaked at 4 wk in control while the gene expression increased gradually after 50% and 100% depodding. The transient up-regulation of ATGs and the decline of leaf N content and SPAD occurred simultaneously. These results indicated that ATGs are involved in leaf senescence and N remobilization from leaf to pod.