Molecular Evidence of Crosstalk Between Bacterial Endophytes and Plant Transcriptome in Brassica juncea

The beneficial effects of endophytes on plant growth, development and yield are well known. Modulating plant growth-promoting substances and ameliorating biotic and abiotic stresses are some of the key mechanisms that are deployed by endophytes to facilitate host growth and defence. However, the understanding of the plant’s genome response to their presence is still limited. Therefore, this study provides an insight into the microbiome of B. juncea seeds as well as leaves, and its impact on plant growth and development. It also correlates their presence with the changes in plant. Removal of seed-borne culturable endophytes resulted in trade-off of accelerated growth with decreased biomass. 16S metagenomics revealed that bacterial endophyte diversity and density varied with stage of the plant. We found that 22 endophytic genera including Enterococcus, Halobacteroides, Planktothrix and Streptomyces were observed irrespective of Bavistin treatment and age of the plant. Removal of culturable endophytes also led to downregulation of crucial genes involved in growth, photosynthesis (Photosystem I assembly protein, Photosystem II reaction center protein and Rubisco), transport (nitrate transporter; NRT) and regulation of plant hormones (auxin homeostasis and signalling; CYP83A1) in B. juncea. To the best of our knowledge, this is the first report of the response of plant’ transcriptome to changes in endophyte composition indicating a strong possibility of host gene regulation by the endophytic partner. The exact mechanism of the same needs to be further explored.