• MjMAP19 and MjMAP40 are amphid-secreted MAP-1 effectors required for early host recognition and invasion. • The two effectors exhibit sharply contrasting transcriptional and thermal-response profiles, revealing regulatory divergence. • Both effectors associate with ER and Golgi compartments and suppress ETI-associated programmed cell death. • Overexpression enhances nematode infection in tomato, with MjMAP40 uniquely promoting giant-cell expansion. • RNAi silencing reduces host recognition and root penetration, confirming essential roles in early parasitism. Root-knot nematodes (RKNs) are among the most destructive plant parasites, relying on effector proteins to manipulate host physiology and promote infection. The Meloidogyne avirulent protein-1 (MAP-1) effector family has been implicated in early host–parasite interactions, but its functional roles remain largely undefined. Here, we characterize two M. javanica orthologs, MjMap19 and MjMap40 , identified through oxylipin-induced pre-parasitic J2s (ppJ2s) transcriptomic profiling. Fluorescence in situ hybridization localized both transcripts to the amphids of ppJ2s, supporting a role in sensory signaling. Gene-expression analysis revealed strong induction at the ppJ2 stage, followed by marked downregulation during early parasitism, with a sharper induction and decline for MjMap40 . Subcellular localization in planta showed that MjMAP19 and MjMAP40 associate with endomembrane compartments, including the endoplasmic reticulum and Golgi, alongside cytoplasmic and nucleoplasmic localization, consistent with an intracellular site of action. Functional assays in Nicotiana benthamiana demonstrated that both effectors suppressed Gpa2/RBP-1–triggered programmed cell death and reduced ion leakage, providing direct evidence that MAP-1 family effectors can suppress ETI-associated defenses. Overexpression of the corresponding genes in tomato hairy roots confirmed the virulence function of the encoded proteins, resulting in enhanced gall formation and nematode reproduction. Corroborating this, in vitro RNAi silencing of MjMap19 and MjMap40 further confirmed their important roles, as knockdown significantly reduced nematode host recognition and root penetration. Together, these results identify MjMAP19 and MjMAP40 as key amphid-associated virulence effectors that suppress host immunity and promote feeding-site development. Despite overlapping functions, their transcriptional dynamics diverge substantially: both MjMap19 and MjMap40 exhibit induction at the ppJ2 stage followed by a decline during the early parasitic stage; however, the amplitude of these expression shifts, both the upregulation and subsequent downregulation, is considerably greater for MjMap40 than for MjMap19 , indicating a markedly sharper transcriptional response. Combined with their contrasting temperature responses, these dynamics suggest distinct evolutionary trajectories: MjMap19 retains expression and functional activity under elevated temperatures, potentially securing virulence where Mi-1 resistance is compromised, whereas MjMap40 lacks temperature responsiveness and displays features consistent with structural and regulatory reduction. These contrasting roles highlight how effector diversification enables RKNs to fine-tune host manipulation, offering new mechanistic insights into nematode adaptation, parasitic success, and resistance breakdown.
Hada et al. (Sun,) studied this question.