Distinctive Physio-Biochemical Properties and Transcriptional Changes Unfold the Mungbean Cultivars Differing by Their Response to Drought Stress at Flowering Stage

Mungbean is a nutritionally and economically important pulse crop cultivated around Asia, mainly in India. The crop is sensitive to drought at various developmental stages of its growing period. However, there is limited or almost no research on a comparative evaluation of mung-bean plants at the flowering stage under drought conditions. Hence, the aim of this research was to impose the drought stress on two mungbean cultivars VRM (Gg) 1 and CO6 at the flowering stage and assess the physio-biochemical and transcriptional changes. After imposing the drought stress, we found that VRM (Gg) 1 exhibited a low reduction in physiological traits (Chlorophyll, relative water content, and plant dry mass) and high proline content than CO6. Additionally, VRM (Gg) 1 has a low level of H2O2 and MDA contents and higher antioxidant enzymes (SOD, POD, and CAT) activity than CO6 during drought stress. The transcriptional analysis of photosynthesis (PS II-PsbP, PS II-LHC, PS I-PsaG/PsaK, and PEPC 3), antioxidant (SOD 2, POD, CAT 2), and drought-responsive genes (HSP-90, DREB2C, NAC 3 and AREB 2) show that VRM (Gg) 1 had increased transcripts more than CO6 under drought stress. Taken together, VRM (Gg) 1 had a better photosynthetic performance which resulted in fewer reductions in chlorophyll, relative water content, and plant dry mass during drought stress. In addition, higher antioxidative enzyme activities led to lower H2O2 and MDA levels, limiting oxidative damage in VRM (Gg) 1. This was positively correlated with increased transcripts of photosynthesis and antioxidant-related genes in VRM (Gg) 1. Further, the increased transcripts of drought-responsive genes indicate that VRM (Gg) 1 has a better genetic basis against drought stress than CO6. These findings help to understand the mungbean response to drought stress and will aid in the development of genotypes with greater drought tolerance by utilizing natural genetic variants.