Background Helicoverpa armigera is a major insect pest of several crop plants, including pigeonpea. Resistant gene sources are not available in the cultivated gene pool, but resistance has been observed in its crop wild relative, Cajanus scarabaeoides. Gene regulatory mechanisms governing the systemic immune response of this plant to pod borer infestation have not yet been deciphered. MicroRNA (miRNA) profiles of H. armigera‐infested and undamaged adjacent leaves of C. scarabaeoides were compared to gain an insight into the plant–insect interactions and to identify dynamic miRNA molecules potentially acting as mediators of systemic defence responses. Results A total of 211 conserved, temporally dynamic miRNA were identified in the unfed adjacent leaves, out of which 98 were found to be differentially expressed in comparison to control leaves. On further analysis, most of the miRNA detected in the adjacent leaves was found to target genes involved in the defence pathways and plant immune response. An overlap of the differentially expressing miRNAs was observed between insect‐fed and adjacent unfed leaves, indicating the transmission of signal from the site of infestation to the undamaged parts of the plant, indicative of induction of a systemic defence response. Conclusion The miRNA response in the unfed leaves had the signatures of induced changes in metabolism and signal transduction for induction of defence pathway genes. This study reveals the participation of miRNAs in imparting pod borer resistance and mounting a systemic defence response against pod borer infestation in C. scarabaeoides. © 2022 Society of Chemical Industry.

The polyphagous insect pest, Helicoverpa armigera, is a detriment to crop productivity. Host-delivered RNAi has emerged as a potential tool to complement Bt technology for controlling insect pest menace. In this study transgenic tobacco ( Nicotiana tabacum L.; cv. Petit Havana) plants expressing dsRNA targeting the H. armigera gene, HaAce1 , encoding the major isoform of acetylcholinesterase, were developed. A 643 nucleotide RT-PCR amplified HaAce1 cDNA fragment was ligated in sense and antisense orientation intervened by GBSS intron to develop an inverted repeat (IR) gene construct. The HaAce1 IR gene construct (IR- Ace1 ) under the transcriptional control of CaMV 35S promoter and NOS terminator was used for Agrobacterium -mediated transformation of tobacco leaf disc explants. Fourteen HaAce1- hpRNA tobacco transgenic lines were obtained after screening of 31 putative transformants by PCR and RT-PCR. Five HaAce1- hpRNA tobacco transgenic lines demonstrated high level of resistance against H. armigera larvae based on detached leaf insect bioassay. These selected five tobacco transgenic lines carried two to four copies of the transgene . Generation of HaAce1 -specific siRNA was detected in these tobacco transgenic lines. Semi-quantitative PCR revealed many-fold reductions in the steady-state level of HaAce1 mRNA in larvae fed on leaves of the selected transgenic tobacco lines compared to that in control tobacco leaf-fed larvae. Our findings demonstrate that the host delivered dsRNA targeting Ace1 gene could be a promising strategy for controlling insect pest menace in crops.

Domain of Unknown Function 740 (DUF740) is a gene family that has not been functionally elucidated in rice, until now. We investigated the function of rice DUF740 gene family member, LOC_Os04g59420 ( OsSRDP-OryzasativaStress Responsive DUF740 Protein) which showed upregulation in response to drought stress in the available global expression data. Transgenic plants of OsSRDP gene, driven by a stress-inducible promoter AtRd29A, were developed in the background of a drought stress sensitive rice cv. Pusa Sugandh 2 (PS2) and their transgene integration and copy number were confirmed by molecular analysis. Homozygous transformants showed better resilience than PS2 when subjected to drought, salinity and cold stresses but not heat stress. Transgenic plants maintained higher RWC, photosynthetic pigments and proline accumulation under drought and salinity stresses. Further, they exhibited less accumulation of reactive oxygen species (ROS) than PS2 under drought stress as seen from the transcript abundance studies of the ROS genes. Under cold stress, OsSRDP transgenic lines illustrated minimal cell membrane injury than PS2. Additionally, the transgenic plants showed resistance to virulent strain of rice blast fungus Magnaporthe oryzae. Altogether, our findings established that stress-inducible expression of OsSRDP can significantly enhance tolerance to multiple abiotic stresses and a biotic stress.