Silencing Autophagy-Related Gene 2 (ATG2) Results in Accelerated Senescence and Enhanced Immunity in Soybean

Abstract

Autophagy plays a critical role in nutrient recycling and stress adaptations. However, the role of autophagy has not been extensively investigated in crop plants. In this study, soybean autophagy-related gene 2 (GmATG2) was silenced, using virus-induced silencing (VIGS) mediated by Bean pod mottle virus (BPMV). An accelerated senescence phenotype was exclusively observed for the GmATG2-silenced plants under dark conditions. In addition, significantly increased accumulation of both ROS and SA as well as a significantly induced expression of the pathogenesis-related gene 1 (PR1) were also observed on the leaves of the GmATG2-silenced plants, indicating an activated immune response. Consistent with this, GmATG2-silenced plants exhibited a significantly enhanced resistance to Pseudomonas syringae pv. glycinea (Psg) relative to empty vector control plants (BPMV-0). Notably, the activated immunity of the GmATG2-silenced plants was independent of the MAPK signaling pathway. The fact that the accumulation levels of ATG8 protein and poly-ubiquitinated proteins were significantly increased in the dark-treated GmATG2-silenced plants relative to the BPMV-0 plants indicated that the autophagic degradation is compromised in the GmATG2-silenced plants. Together, our results indicated that silencing GmATG2 compromises the autophagy pathway, and the autophagy pathway is conserved in different plant species.

Silencing GmBIR1 in Soybean Results in Activated Defense Responses

“…Through BPMV-VIGS silencing approach, we successfully identified both positive and negative regulators of defense responses in soybean [20][21][22][23][24][25]. Using the same strategy, we found that when Glyma.18g246400 was silenced, a significantly stunted stature (Figure 1A) and spontaneous cell death on the systemic leaves were observed for the silenced plants (Figure 1B).…”

“…Activated defense responses are usually correlated with enhanced disease resistance [20][21][22][23][24][25]. To examine whether disease resistance is enhanced in GmBIR1-silenced plants, SMV strain N tagged with the GUS marker protein (SMV-N-GUS) [33] was inoculated via biolistic bombardment onto three individual leaves collected from both the vector control plants and the GmBIR1-silenced plants.…”

“…The autoimmune phenotype of the GmBIR1-silenced plants (Figure 1B) actually is a result of cosilencing of both GmBIR1a and GmBIR1b. We have previously shown that multiple copies of GmMPK4, GmMPK6, GmMEKK1, GmFLS2, and GmATG2 genes could be successfully cosilenced using a single BPMV-VIGS construct [20,[22][23][24][25]. Given that soybean is polyploidy and is recalcitrant to transformation, VIGS is currently one of the most efficient approaches to interrogate gene functions in soybean [26,27].…”

“…Although extensively studied in the model plant Arabidopsis, the investigations of RLKs in crop plants are limited. Using the BPMV-VIGS system, we have recently identified multiple positive and negative regulators of defense responses in soybean [20][21][22][23][24][25]. Here, using the same strategy, we identified GmBIR1 as a negative regulator of defense responses in soybean.…”

Vacuolar Processing Enzymes in Plant Programmed Cell Death and Autophagy

“…Moreover, bacteria and viruses can also be degraded in the infected cells through this process [ 70 ]. Autophagy takes place in all life stages of the plant, including development, senescence, and cell death [ 12 , 71 ]. Under normal development and growth conditions, the insensitivity of autophagy is relatively low—basal.…”