Increased root growth and seed yield in transgenic soybean overexpressing NAC genes GmNAC19 and GmGRAB1

Soybean NAC genes GmNAC19 and GmGRAB1 are root-preferential expressed genes whose overexpression led to enhanced root growth and/or tolerance to dehydration stress in transgenic soybean plants. Soybean (Glycine max) is one of the most important crops globally. Water shortage stress is a major abiotic factor limiting soybean growth and production. NAC transcription factors play important roles in plant development and stress responses. To date, numerous soybean NAC genes for plant growth and stress tolerance were identified. Yet, the functionality of the vast majority of them remains unknown. We previously identified soybean NAC genes GmNAC19 and GmGRAB1 whose overexpression enhanced root growth and/or dehydration tolerance in transgenic soybean hairy root system. Here, we examined the functionality of these genes through transgenic overexpression in homozygous T₃ soybean lines. The endogenous expression analyses showed detectable levels of expression for both genes in leaf, stem, and root tissues with the highest levels in roots, suggesting their importance in roots. Under non-stress conditions, GmNAC19- and GmGRAB1-overexpressing plants had up to 1.7-fold increase in root length and/or 1.3-fold increase in root fresh/dry weight. There was a positive association between the level of increasing GmNAC19 and GmGRAB1 expression and root growth in the transgenic plants. The transgenic plants with improved root growth also produced higher seed yield by 1.5-fold than control plants, suggesting a positive impact of the increased root growth on seed production. Furthermore, GmNAC19-overexpressing plants showed an improved survival rate under water-deficit stress. The present study provides further insights into the potential applications of these NAC genes for development of improved soybeans.