Revealing drought tolerance mechanisms in Pongamia pinnata through integrated physiological, biochemical, and transcriptomic profiling

Abstract

Pongamia pinnata is a promising industrial species for biofuel production. However, the detrimental effects of drought stress on the initial growth phases pose significant challenges to germination and seedling development. This problem impedes the establishment of commercial plantations in drought-prone areas, primarily because of the lack of cultivar stability. To address this issue, understanding their physiochemical and molecular responses is crucial. To elucidate the intricate molecular mechanisms underlying drought tolerance, two contrasting Pongamia genotypes, NRCP9 (tolerant) and NRCP10 (sensitive), were subjected to drought stress and watered conditions. Drought stress significantly reduced the chlorophyll content and relative water content in the NRCP10 (susceptible) genotype. In contrast, drought stress induced greater increases in peroxidase activity and proline accumulation in NRCP9 than in NRCP10. Furthermore, transcriptome analysis revealed a total of 26,195 and 18,742 differentially expressed genes (DEGs) in the tolerant and susceptible genotypes, respectively. Additionally, 128 common DEGs were commonly expressed under drought stress conditions, whereas 10,271 DEGs were commonly expressed under well-watered conditions. Among the DEGs in the TF families, the major were bHLH, NAC, ERF, WRKY, MYB, Trihelix, bZIP, FAR1, B3, C3H, STAT, and C2H2. Furthermore, transcriptome analyses revealed the significant genes involved in hormone biosynthesis, secondary metabolite accumulation, cofactor and carbon metabolism, and MAPK signaling. Additionally, the selected genes were validated by qRT-PCR, the transcriptome analysis and expression patterns were found to be corresponded. These findings reveal Pongamia's stress-adaptive mechanism and shed light on the physicochemical and differential gene responses to drought stress.