Abstract
Legume species are recognized for their nutritional benefits and contribution to the sustainability of agricultural systems. However, their production is threatened by biotic constraints with devastating impacts on crop yield. A deep understanding of the molecular and genetic architecture of resistance sources culminating in immunity is critical to assist new biotechnological approaches for plant protection. In this review, the current knowledge regarding the major plant immune system components of grain and forage legumes challenged with obligate airborne biotrophic fungi will be comprehensively evaluated and discussed while identifying future directions of research. To achieve this, we will address the multi-layered defense strategies deployed by legume crops at the biochemical, molecular, and physiological levels, leading to rapid pathogen recognition and carrying the necessary information to sub-cellular components, on-setting a dynamic and organized defense. Emphasis will be given to recent approaches such as the identification of critical components of host decentralized immune response negatively regulated by pathogens while targeting the loss-of-function of susceptibility genes. We conclude that advances in gene expression analysis in both host and pathogen, protocols for effectoromics pipelines, and high-throughput disease phenomics platforms are rapidly leading to a deeper understanding of the intricate host-pathogen interaction, crucial for efficient disease resistance breeding initiatives.
Highlights
Grain and forage legume species comprise the largest source of plant-based proteins, both for human and livestock consumption, especially in poorer areas where meat, fish, and dairy are economically inaccessible [1]
Such reorganization of cytoplasmic content have been described by Chen and Heath [60] in an attempt to uncover the main cytological events culminating in hypersensitivity of cowpea leaf epidermal cells induced by cowpea rust pathogen (Uromyces vignae)
While the apoplastic hydrolysis of sucrose through the secreted fungal invertase in early infection structures promote the conversion of infected tissue from source to sink and limit the export of carbohydrates from the infected tissue, the increased activity of these enzymes in the extra-haustorial matrix allows for a supply of substrate for the fungi carbohydrates transporters [95]
Summary
Grain and forage legume species comprise the largest source of plant-based proteins, both for human and livestock consumption, especially in poorer areas where meat, fish, and dairy are economically inaccessible [1]. Even in cases of germ tubes capable to locate and penetrate the stomata complexes, only 50% developed a normal substomatal vesicle (SSV), while the remaining contained aberrant SSV or did not have SSV structure This observation might be due to marked differences in the topographic features and biochemical composition of epicuticular waxes in V. faba leaves compared to wheat. In M. truncatula accessions infected with the adapted U. striatus (pathogens able to infect and develop appropriate infection structures and to overcome resistance barriers from the infected plant) and the non-adapted U. fabae and U. lupinicolus rust pathogens (pathogens less effective to overcome inducible or structural defense barriers), germ tubes of the three pathogens had a similar level of success in forming appressoria over stoma [31] In this case, pre-invasive resistance mechanisms were of marginal importance in reducing infection severity
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