NLRs in plants.

Intracellular immune receptors with nucleotide-binding, leucine-rich domains (NLRs) are found in both plants and animals. Compared to animals, NLR-encoding gene families are expanded, more prevalent and have enriched diversity in higher plants. Strong host defense triggered by the recognition of specific pathogen effectors constitutes a major part of the plant immune response that has long been exploited to breed crops for enhanced resistance. Although the first plant NLR genes were cloned about 20 years ago, their signaling mechanisms remain obscure. Here we review recent progress in plant NLR studies, focusing on their pathogen recognition, homeostasis control and potential signaling activation mechanisms.