Chitin recognition in rice and legumes

This review focuses on a comparison of plant reception of chitin oligosaccharides by legumes and rice. Chitin oligosaccharides (dp=6-8) released from fungal pathogens induce plant defense reactions in rice, while lipo-chitin oligosaccharides (dp=4-5) induce the development of a new plant organ, the nodule, in legumes during infection by rhizobia. The former situation is pathogenic and the latter situation beneficial to the plant. However, these two systems do share some common features. We hypothesize that rice and legumes, as well as other plants, may possess members of an evolutionarily conserved family of chitin binding proteins. These proteins may play an important role in chitin reception and subsequent signal transduction. However, data support the idea that legumes may possess a second chitin binding receptor that shows a greater specificity for the lipo-chitin nodulation signals. The presence of this second receptor may be one of the key factors that distinguishes plants capable of nodulation by rhizobia (e.g., soybean) from those that cannot be nodulated (e.g., rice).