Defensin gene family in Medicago truncatula: structure, expression and induction by signal molecules

Abstract

A large gene family encoding the putative cysteine-rich defensins was discovered in Medicago truncatula. Sixteen members of the family were identified by screening a cloned seed defensin from M. sativa (Gao et al. 2000) against the Institute for Genomic Research's (TIGR) M. truncatula gene index (MtGI version 7). Based on the comparison of their amino acid sequences, M. truncatula defensins fell arbitrarily into three classes displaying extensive sequence divergence outside of the eight canonical cysteine residues. The presence of Class II defensins is reported for the first time in a legume plant. In silico as well as Northern blot and RT-PCR analyses indicated these genes were expressed in a variety of tissues including leaves, flowers, developing pods, mature seed and roots. The expression of these genes was differentially induced in response to a variety of biotic and abiotic stimuli. For the first time, a defensin gene (TC77480) was shown to be induced in roots in response to infection by the mycorrhizal fungus, Glomus versiforme. Northern blot analysis indicated that the tissue-specific expression patterns of the cloned Def1 and Def2 genes differed substantially between M. truncatula and M. sativa. Furthermore, the induction profiles of the Def1 and Def2 genes in response to the signaling molecules methyl jasmonate, ethylene and salicylic acid differed markedly between these two legumes.

Plant defensins and virally encoded fungal toxin KP4 inhibit plant root growth

“…However, MsDef1 and MtDef2 defensins are not expressed in the roots of Medicago spp. (Hanks et al 2005) and are unlikely to have a role in inhibiting the root growth of other plants. Some of these defensins may act as bioactive plant peptide signals much like other small extracellular signaling proteins such as CLAVATA3 (Fletcher et al 1999;Lenhard and Laux 2003;Rojo et al 2002;Trotochaud et al 2000), RALF (Pearce et al 2001), SCR/SP11 (Schopfer et al 1999;Takayama et al 2000), PSK (Matsubayashi and Sakagami 1996), and Systemin (Pearce et al 2001).…”

Plant defensins

“…2,10,20 In addition to pathogen-induction, defensins can also be induced by environmental stress, such as drought, salt and cold, 2 and the signaling molecules, such as methyl jasmonate, ethylene and salicylic acid. 21 The expression of the defensins induced in response to a variety of biotic and abiotic stimuli provides examples of cross-talk between signal transduction pathways and gene expression programs. 2 The generation of transgenic tomato plants constitutively expressing the chili defensin (cdef1) gene resulted in enhanced resistance against Phytophthora infestans and Fusarium sp.…”

Differentially expressed genes in healthy and plum pox virus-infected Nicotiana benthamiana plants

“…Signaling pathways controlling these plant responses to microbial infection operate through the action of phytohormones like jasmonic acid (JA). During viral infection, however, JA-regulated gene expression is rather suppressed by RNA silencing (Hanks et al, 2005;Westwood et al, 2014). As a consequence, virus-infected plants may be more susceptible to secondary bacterial or fungal infections.…”