Abstract
Antimicrobial cationic peptides (AMPs) are ubiquitous small proteins used by living cells to defend against a wide spectrum of pathogens. Their amphipathic property helps their interaction with negatively charged cellular membrane of the pathogen causing cell lysis and death. AMPs also modulate signaling pathway(s) and cellular processes in animal models; however, little is known of cellular processes other than the pathogen-lysis phenomenon modulated by AMPs in plants. An engineered heterologous AMP, msrA3, expressed in potato was previously shown to cause resistance of the transgenic plants against selected fungal and bacterial pathogens. These lines together with the wild type were studied for growth habits, and for inducible defense responses during challenge with biotic (necrotroph Fusarium solani) and abiotic stressors (dark-induced senescence, wounding and temperature stress). msrA3-expression not only conferred protection against F. solani but also delayed development of floral buds and prolonged vegetative phase. Analysis of select gene transcript profiles showed that the transgenic potato plants were suppressed in the hypersensitive (HR) and reactive oxygen species (ROS) responses to both biotic and abiotic stressors. Also, the transgenic leaves accumulated lesser amounts of the defense hormone jasmonic acid upon wounding with only a slight change in salicylic acid as compared to the wild type. Thus, normal host defense responses to the pathogen and abiotic stressors were mitigated by msrA3 expression suggesting MSRA3 regulates a common step(s) of these response pathways. The stemming of the pathogen growth and mitigating stress response pathways likely contributes to resource reallocation for higher tuber yield.
Highlights
Sustained plant losses due to microbial diseases cause crop yield reduction and are of major economical concern to farmers and agriculture industry [1,2]
We demonstrate here that expression of an antimicrobial peptide, MsrA3, in potato provides resistance against the pathogen F. solani, mitigates plant defense responses including hypersensitive response (HR), reactive oxygen species (ROS), leaf senescence and wounding, and alters timing of bud development, which culminates in increased yield of the two transgenic potato lines
While Antimicrobial cationic peptides (AMPs) are known to be directly toxic to plant pathogens [54,57,58,59], as was evident here for MsrA3 potato - F. solani interaction, we show that msrA3 expression causes delayed floral development and suppresses the normal defense pathways of plants in response to a few abiotic-type stressors
Summary
Sustained plant losses due to microbial diseases cause crop yield reduction and are of major economical concern to farmers and agriculture industry [1,2]. The dynamics of plant response to a disease(s) change with environmental interactions [4], requiring an indepth understanding of the molecular mechanisms involved. HR is accompanied by an oxidative burst due to reactive oxygen species (ROS) [10], and changes in defense-related gene transcripts [11] Metabolites such as glycerol-3-phosphate [12] and pipecolic acid [13] and hormones such as ethylene, salicylic acid (SA), jasmonates (JAs), nitric oxide (NO) and abscisic acid (ABA) have been implicated in plant immunity through regulating SAR [14]. The NLR receptor family-triggered immunity seems conserved across plant lineages and it was suggested that NLR could interact with different host proteins to mediate distinct resistance responses [21,22]. Expression of pepper Bs2 resistance (R) gene, which recognizes AvrBs2 effector released by Xanthomonas sp, was shown to provide field level resistance to the bacterial spot disease in transgenic tomatoes [23]
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