Abstract
The thickening of Zizania latifolia shoots, referred to as gall formation, depends on infection with the fungal endophyte Ustilago esculenta. The swollen and juicy shoots are a popular vegetable in Asia. A key role for cytokinin action in this process was postulated. Here, trans-zeatin stimulated swelling in fungi-infected Z. latifolia. A two-component system (TCS) linked cytokinin binding to receptors with transcriptional regulation in the nucleus and played important roles in diverse biological processes. We characterized 69 TCS genes encoding for 25 histidine kinase/histidine-kinase-like (HK(L)) (21 HKs and 4 HKLs), 8 histidine phosphotransfer proteins (HP) (5 authentic and 3 pseudo), and 36 response regulators (RR; 14 type A, 14 type B, 2 type C, and 6 pseudo) in the genome of Z. latifolia. These TCS genes have a close phylogenetic relationship with their rice counterparts. Nineteen duplicated TCS gene pairs were found and the ratio of nonsynonymous to synonymous mutations indicated that a strong purifying selection acted on these duplicated genes, leading to few mutations during evolution. Finally, ZlCHK1, ZlRRA5, ZIRRA9, ZlRRA10, ZlPRR1, and ZlPHYA expression was associated with gall formation. Among them, ARR5, ARR9, and ZlPHYA are quickly induced by trans-zeatin, suggesting a role for cytokinin signaling in shoot swelling of Z. latifolia.
Highlights
Zizania latifolia belongs to the wild rice genus Zizania and was an important grain crop in ancientChina
Chan and Thrower [7] suggested that three kinds of cytokinins including zeatin and zeatin riboside were isolated in Z. latifolia gall tissue, and Ustilago esculenta could produce zeatin in culture
To obtain a better understanding of the functions of the two-component system (TCS) genes, we investigated their transcriptional levels in the different gall formation stages in Z. latifolia
Summary
Zizania latifolia belongs to the wild rice genus Zizania and was an important grain crop in ancient. Around 2000 years ago, Z. latifolia was infected by the fungal endophyte Ustilago esculenta which causes swelling in shoot apical tissues, resulting in juicy galls. Z. latifolia are a popular vegetable in China (called “Jiaobai”), East Asian countries, and Japan [1,2]. Plant tumors or “galls” can be induced by different pathogens such as bacteria, viruses, fungi, protists, and insects. Despite different pathogenic mechanism to induce galls, most of these plant pathogens demonstrate the ability to change the phytohormone level in the host plants, especially cytokinins. The well-studied gall-forming Agrobacterium tumefaciens carries the
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