Insights into the Origin and Evolution of the Plant Hormone Signaling Machinery

Abstract

Plant hormones modulate plant growth, development, and defense. However, many aspects of the origin and evolution of plant hormone signaling pathways remain obscure. Here, we use a comparative genomic and phylogenetic approach to investigate the origin and evolution of nine major plant hormone (abscisic acid, auxin, brassinosteroid, cytokinin, ethylene, gibberellin, jasmonate, salicylic acid, and strigolactone) signaling pathways. Our multispecies genome-wide analysis reveals that: (1) auxin, cytokinin, and strigolactone signaling pathways originated in charophyte lineages; (2) abscisic acid, jasmonate, and salicylic acid signaling pathways arose in the last common ancestor of land plants; (3) gibberellin signaling evolved after the divergence of bryophytes from land plants; (4) the canonical brassinosteroid signaling originated before the emergence of angiosperms but likely after the split of gymnosperms and angiosperms; and (5) the origin of the canonical ethylene signaling pathway postdates shortly the emergence of angiosperms. Our findings might have important implications in understanding the molecular mechanisms underlying the emergence of land plants.

On plant defense signaling networks and early land plant evolution

“…The PP pathway is also a source for SA biosynthesis [122]. Moreover, potential homologs for the SA receptor Nonexpressor of PR genes 1 (NPR1) [123], were reported for all land plants [113] and the putative NPR1 homolog of P. patens can partially complement defense signaling-associated phenotypes of the Arabidopsis npr1 mutant [124]. As for ET, recent studies showed that streptophyte algae produce, sense and respond to ET [112,115], but these studies did not dissect the role of ET as a hormone involved in defense.…”

Microbial production of plant hormones: Opportunities and challenges

“…[7][8][9][10] Plant hormones are found not only in higher plants, but also in algae, and in plant-associated bacteria and fungi. [11][12][13] However, in this case, plant hormones are not the essential small molecular necessary to the growth and reproduction of the microorganisms. Thus they are regarded as secondary metabolites.…”

Parasitic Plants <i>Striga</i> and <i>Phelipanche</i> Dependent upon Exogenous Strigolactones for Germination Have Retained Genes for Strigolactone Biosynthesis

“…In addition, SLs may regulate shoot branching patterns in parasites just as in other eudicots, and Liu et al [33] suggest that SLs are important in regulating branching in Striga. SL hormones are evolutionarily ancient and understanding of their role in coordinating plant development is rapidly expanding [14] [32]. The current work contributes to this body of knowledge by demonstrating that parasitic plant synthesis of SLs and use as germination triggers is likely more sophisticated than initially expected.…”

“…The origin of AM fungi symbiosis and shoot branching is ancient [11], and there is evidence that all angiosperms and even lower plants such as mosses and liverworts produce SLs [12]- [14]. However, the requirement of Orobanche, Phelipanche and Striga for exogenous SLs raises questions about how these species have evolved to respond to exogenous SLs and whether this trait could involve a loss in SL biosynthetic ability [15].…”