Early responses of the marine diatom Phaeodactylum tricornutum to herbivory-related decadienal : effects on the transcriptome, proteome and regulatory mechanisms of two light harvesting complex genes

Worldwide food security is based on crop production which largely depends on plants’ stress tolerance capacities at the onset of diverse biotic and abiotic stresses. Photosynthetic organisms have developed many sophisticated defense responses that balance maintenance of central metabolic processes such as photosynthesis with new metabolic demands for acclimation to the stress. However, in both higher plants and algae, how central metabolic pathway-related genes are regulated and the functional significance of the adjustments are poorly understood. Marine diatoms are known to cope with continuous challenges of stress in the ocean and can provide general insights on the roles of rapid photosynthetic and core carbon metabolism gene expression changes in acclimation. During zooplankton grazing, damaged diatom cells release polyunsaturated aldehyde (PUA) from membranes, which impair reproduction in grazers and at the same time affect neighboring undamaged diatoms. In response to PUA, undamaged diatoms cells exhibit remarkable alteration in the photosynthesis-related gene expression. In this study, early response dynamics in the marine diatom Phaeodactylum tricornutum were investigated in response to sublethal concentrations of a model PUA, 2-E, 4-E/Z-decadienal (DD). Genome-wide analysis showed mRNAs encoding photosynthetic Light Harvesting Complex (LHC) antenna proteins were differentially downregulated except for a few upregulated mRNAs at 3 and 6 h of DD treatments. Our findings revealed gene regulatory mechanisms of two differentially regulated LHC transcripts. In cells treated with DD, he downregulation of Lhcf2 mRNA was due to reduced transcription and increased mRNA turnover, and Lhcf15 upregulation depended on increased transcription and mRNA stability. Further, I compared changes in the transcriptome and proteome, especially for photosynthesis-and central carbon metabolism-related pathways to investigate early molecular responses during short-term sublethal DD treatment. The majority of the differentially expressed transcripts involved in photosynthetic light harvesting, chlorophyll biosynthesis were downregulated and central carbon metabolism exhibited a mixed expression. In contrast, few of the corresponding proteins exhibited differential expression. Thus, during the early exposure to DD, proteins involved in photosynthesis-and energyrelated pathway remained predominantly stable despite extensive differential expression of their encoding transcripts. I have postulated that transient suppression of transcripts is an early defense response to save energy and resources to support synthesizing important components needed for acclimation to DD induced stress. Hence, our study provides novel insight into the photosynthetic gene regulatory mechanism and metabolic network reprogramming during early stress response of herbivory-related DD stress condition.Plant Biolog