Isolation and expression analysis of a cobalamin-independent methionine synthase gene from the parasitic plant Orobanche ramosa

Broomrapes (Orobanche spp) are holoparasitic weeds that cause devastating losses in many economically important crops. The branched broomrape (Orobanche ramosa) represents a real threat for many vegetable crops including tobacco, tomato and potato.During its parasitic phase (tubercles and flowers), Orobanche behaves like an additional sink of the host and competes with other actively growing parts of the host plant for photoassimilates. In order to elucidate molecular mechanism that are implicated in the tubercles and flowers formation, a gene involved in sink development was studied.In this work, the cobalamin-independent methionine synthase clone Or-MET1 was isolated from a cDNA library representing different developmental stages of the parasitic plant. The pattern of expression of the gene was studied by quantitative RT-PCR analysis during both pre-infection and parasitic phases. Since this gene is sucrose-regulated in plants, the effect of this sugar in Or-MET1 expression was also analysed. The results showed that Or-MET1 was expressed during all the stages tested but was more prominently induced in tubercles and flowers. No effect of sucrose was observed. These findings are consistent with a typical gene expression pattern of cobalamin-independent methionine synthase in host sink and with a putative role of Or-MET1 during post-infection stages.