Abstract
The molecular basis of phloem tissue development and function is largely unknown, although the phloem tissue plays important roles in sugar translocation and long-distance signaling. We have found that a Zinnia HD-Zip gene, ZeHB3, is expressed specifically in immature phloem cells. The overexpression of either ZeHB3 or its Arabidopsis homolog, AtHB5, in Arabidopsis causes the disappearance of the starch granules at the root cap and seedling lethal phenotype. These genes induced ectopic expression of a phloem marker gene, SUC2::GUS, but not other phloem markers, such as AHA3::GUS and APL::GUS. Since the SUC2 encodes a sucrose transporter that is important for the efficient phloem transport, it is possible that the ZeHB3 and AtHB5 are associated with maintenance of phloem function. The downstream analysis of the ZeHB3 and AtHB5 by using microarray analysis and suppressor screening of the overexpressors will also be reported.
