The nodulation and yield paradox: 35S:VlMYBA2 transgenic background enhances mung bean nodulation with Bacillus sp.
N V T Jayaprada1, W M K S B Abesekara2, S Geekiyanage3
1Board of Study in Agriculture, Faculty of Graduate Studies, University of Ruhuna, Matara, Sri Lanka.
Abstract:
Both plant MYB transcription factors and plant growth promoting bacteria (PGPB) regulate biotic stress responses and crop productivity. However, their potential antagonistic cross-talk or synergistic priming effects remain unclear. The potential function of VlMYBA2 in transgenic mung bean was investigated through in silico analysis to assess the interaction potential of both mung bean VrMYB90 and VlMYBA2 with bHLH proteins involved in transcriptional complexes. A pot experiment was conducted under greenhouse conditions using a completely randomized design to evaluate the effect of PGPB, Bacillus sp. I-I on 35S:VlMYBA2 mung bean. Treatments, each with three replicates, included transgenic plants (V), Bacillus sp. I-I-inoculated wild-type (I), inoculated V (VI), inorganic fertilizer treatment (F), and a non-inoculated control (C). Three independent transgenic lines were developed through Agrobacterium-mediated transformation. Treatments were evaluated for anthocyanin accumulation, growth, yield, molecular confirmation, and soil N, P and K status. Data were analyzed using one-way ANOVA followed by Tukey's test at p < 0.05. PCR confirmed the presence of VlMYBA2 in purple seedlings, while transgenic plants produced purple pigmentation on stems, racemes, and pods under greenhouse conditions. Nodule numbers were higher in V (43.6 ± 4.01) and VI (45.7 ± 8.87) than in I (26.3 ± 1.2) and C (24.0 ± 1.5) (p < 0.05). Pod number (15.0 ± 2.0), seed number (91.8 ± 5.5), and seed weight per plant (4.94 ± 0.21 g) in I, were greater than those of C (p < 0.05). Soil analysis revealed higher phosphorus (10.05-15.55 ppm), potassium (194.34-239.01 ppm), and nitrogen (0.245-0.333%) levels in the I, F, V, and VI compared with C (p < 0.05). Overall, I-I enhanced yield and soil nutrient availability, whereas V, either alone or VI, did not improve yield suggesting a trade-off between increased nodulation and yield. Future studies should focus on optimizing 35S:VlMYBA2-PGPB interactions to balance enhanced nodulation and nutrient uptake with yield stability.
