Taking Advantage of Plant Defense Mechanisms to Promote Human Health. The Plant Immune System. First of Two Parts

Despite the evidence that plants do not possess sessile cells, they are able to mount a vigorous immune response against invaders or under stressful conditions. Plants are endowed with pattern recognition receptors (PPRs) which perceive damage-associated molecular patterns and microbe- associated molecular patterns or pathogen-associated molecular patterns (PAMPs), respectively. PPR activation leads to either the initiation of PAMP-triggered immunity (PTI) (early response) or the effector-triggered immunity (ETI). Both PTI and ETI contribute to plant systemic acquired resistance as an expression of immunological memory or trained immunity. PTI is initiated by activation of both receptor-like kinases and receptor-like proteins, while ETI depends on nucleotide- binding leucine-rich-repeat protein receptors for microbe recognition. Plant chloroplasts contribute to both PTI and ETI through the production of peptides, which act as hormones or phytocytokines. Salicylic acid, jasmonic acid and ethylene are the major compounds involved in plant defense. The interaction between plant receptors and/or their products and bacterial components will be discussed. Also, emphasis will be placed on plant microbiome for its contribution to plant immune response. Finally, the mutual interplay between insects and plants will also be illustrated. A better knowledge of plant immunity may pave the way for the exploitation of plant derivatives in the field of agriculture and medicine, as well.