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Differential Expression of Two Different EeSTM Genes of Leafy Spurge (Euphorbia esula) and Root-directed Expression from EeSTM Promoter in Leafy Spurge and Arabidopsis

Vijaya K. Varanasi, Wun S. Chao, James V. Anderson and David P. Horvath

SHOOTMERISTEMLESS (STM) encodes a member of the class I KNOX homeodomain protein family that is required for meristem development and maintenance. Leafy spurge is a model perennial weed that produces adventitious meristems on its roots and hypocotyl. These buds are capable of displaying para-, endo- and ecodormancy. We have cloned two different full length cDNAs of STM (EeSTM1 and EeSTM4) from leafy spurge that displays different tissue specific expression patterns. EeSTM1 gene appears to be expressed only in young root and hypocotyl tissue. EeSTM4 is co-expressed with EeSTM1, but it is also expressed highly in the shoot apical meristem and in mature roots. An EeSTM promoter was able to drive GUS expression in the roots, hypocotyl, and shoot apical meristem of Arabidopsis, whereas the AtSTM promoter only produced GUS expression in the shoot apical meristem. Expression analysis indicates that EeSTM expression is detectable in dormant adventitious buds but is up-regulated within three days following defoliation, a treatment that initiates bud regrowth. Seasonal changes in expression of EeSTM correlated to dormancy status in underground leafy spurge buds were observed.