A Medicago truncatula Cystathionine-β-Synthase-like Domain-Containing Protein Is Required for Rhizobial Infection and Symbiotic Nitrogen Fixation  . Issue 4 (16th February 2016)

• Record Type: Journal Article
• Authors: Sinharoy, Senjuti; Liu, Chengwu; Breakspear, Andrew; Guan, Dian; Shailes, Sarah; Nakashima, Jin; Zhang, Shulan; Wen, Jiangqi; Torres-Jerez, Ivone; Oldroyd, Giles; Murray, Jeremy D.; Udvardi, Michael K.
• Is Part Of: Plant physiology. Volume 170:Issue 4(2016)
• Page Start: 2204
• Page End: 2217
• Publication Date: 2016-02-16
• Subjects: Plant physiology -- Periodicals; Botany -- Periodicals; Periodicals; Electronic journals; 571.2
• DOI: 10.1104/pp.15.01853
• Languages: English
• ISSNs: 0032-0889

Abstract

Abstract : A Cystathionine-β-Synthase like protein, exclusively expressed during Medicago-Rhizobium symbiosis, is required for infection thread propagation and bacterial endocytosis. Abstract: The symbiosis between leguminous plants and soil rhizobia culminates in the formation of nitrogen-fixing organs called nodules that support plant growth. Two Medicago truncatula Tnt1 -insertion mutants were identified that produced small nodules, which were unable to fix nitrogen effectively due to ineffective rhizobial colonization. The gene underlying this phenotype was found to encode a protein containing a putative membrane-localized domain of unknown function (DUF 21) and a cystathionine-β-synthase domain. The cbs 1 mutants had defective infection threads that were sometimes devoid of rhizobia and formed small nodules with greatly reduced numbers of symbiosomes. We studied the expression of the gene, designated M . truncatula Cystathionine - β - Synthase-like1 ( MtCBS 1 ), using a promoter-β -glucuronidase gene fusion, which revealed expression in infected root hair cells, developing nodules, and in the invasion zone of mature nodules. An MtCBS 1-GFP fusion protein localized itself to the infection thread and symbiosomes. Nodulation factor-induced Ca 2+ responses were observed in the cbs 1 mutant, indicating that MtCBS 1 acts downstream of nodulation factor signaling. MtCBS 1 expression occurred exclusively during Medicago -rhizobium symbiosis. Induction of MtCBS 1 expression during symbiosis was found to be dependent on Nodule Inception (NIN ), a key transcription factor that controls both rhizobial infection and nodule organogenesis. Interestingly, the closest homolog of MtCBS 1, MtCBS 2, was specifically induced in mycorrhizal roots, suggesting common infection mechanisms in nodulation and mycorrhization. Related proteins in Arabidopsis have been implicated in cell wall maturation, suggesting a potential role for CBS 1 in the formation of the infection thread wall.