The complex network of plant defense mechanisms in response to various stress conditions is often tightly regulated by multiple transcription factors (TFs). They can alter their target gene expression upon binding to their respective cognate cis-elements. A number of studies have functionally characterized the role of different WRKY TFs in various stress conditions in plants such as Arabidopsis, rice, and tobacco. However, their role in a major C4 crop such as pearl millet remains elusive. In our previous study, we showed that the ectopic expression of the group IId member PgWRKY44 in Arabidopsis provides enhanced tolerance to drought and saline conditions. However, along with in silico promoter analysis, the GUS reporter assays upon salicylic acid and methyl jasmonate application indicated its probable involvement in biotic stress resistance. Transcript profiling has shown enhanced expression of PgWRKY44 during both pathogen infection and phytohormone treatments, suggesting its involvement in hormone-mediated defense pathways. To further investigate its role, we have generated transgenic lines overexpressing PgWRKY44 in both pearl millet and rice, which showed elevated resistance against hemibiotrophic fungus Magnaporthe grisea, as evidenced by reduced lesion formation and significant changes in the expression levels of several defense-related genes. The transgenic lines exhibited elevated expression of key genes in both SA (e.g., NH1, ICS1, and PAD4) and JA (e.g., PR10, LOX, and AOS2) pathways, highlighting a potential role for PgWRKY44 in modulating hormonal crosstalk in regulating defense response against M. grisea infection. Collectively, our findings establish PgWRKY44 as a dual regulator of abiotic and biotic stress responses and demonstrate its utility in engineering disease-resistant, climate-resilient cereal crops.
Saha et al. (Sat,) studied this question.