Differential RNA expression of alpha-expansin gene family members in the parasitic angiosperm Triphysaria versicolor (Scrophulariaceae)

Haustoria are parasitic plant specific organs that locate, attach to, and i nvade host plant tissues. Parasitic species of the Scrophulariaceae develop haustoria on their roots in response to chemical signals released by host plant rents. Haustorium development was induced in vitro in tools of the pa rasitic Scrophulariaceae Triphysaria versicolor by treating them with exuda tes obtained from maize roots, the chemical 2,6-dimethoxybenzoquinone (DMBQ ) or the cytokinin 6-benzylaminopurine (BAP). Morphological responses of T. versicolor roots to these haustoria inducing factors (HIFs) included local ized swelling and epidermal hair proliferation near the root tips. These re sponses were not observed when roots of the non-parasitic Scrophslariaceae Lindenbergia muraria were similarly treated. Because expansin proteins are closely associated with plant cell wall expansion and growth, we examined t he expression of expansin genes in response to HIFs. We isolated cDNAs homo logous to transcripts encoding three distinct alpha -expansin proteins in T . versicolor. Northern-blot analyses indicated that these transcripts were differentially abundant in different tissues. Steady-state levels of two ex pansin transcripts increased in T. versicolor roots exposed to BAP, but not DMBQ or maize root exudates. Expansin transcript abundance also increased in L. muraria in response to BAP treatment. These results suggest that the expansins examined fulfill functions distinct from haustorium development. (C) 2001 Elsevier Science B.V. All rights reserved.