Developmental Regulation of a Gene Coding for a Low-Molecular-Weight Heat Shock Protein during Haustorium Formation in the Seedlings of a Holoparasitic Plant, Cuscuta japonica

Dodder (Cuscuta japonica), a holoparasitic angiosperm, develops haustoria that are essential for parasitism. We have previously demonstrated that in Cuscuta seedlings, haustorial formation could be induced efficiently by cooperative effects of far-red light and tactile stimuli in the absence of any host plant [Tada et al. (1996) Plant Cell Physiol. 37: 1049]. In this study, we performed differential display and isolated several cDNAs that were expressed differentially during haustorium development in the seedlings. Sequence similarities identified one of them as a gene encoding a 17-kDa low-molecular-weight heat shock protein (CJHSP17). Northern blot analysis revealed that CJHSP17 mRNAs constitutively accumulated in the seedlings in the absence of environmental stress, and that the transcripts dramatically decreased to undetectable levels prior to emergence of haustoria upon irradiation with far-red light in the presence of tactile stimuli. When treated with either of the two stimuli, the CJHSP17 transcript levels did not decrease and there was no differentiation of haustoria. Moreover, irradiation of red light immediately after far-red light completely repressed both the decrease of mRNAs and the subsequent formation of haustoria. These observations suggest the involvement of down-regulation of CJHSP17 in haustorium development in Cuscuta seedlings.