The researchers also identified a family of genes, dubbed NEN1-4, which act downstream of NAC045 and NAC086. Although the enucleation process starts in plants with mutations in these genes, it doesn't complete properly.
Control of choline transport essential in phloem
A genetic screen identified the CHER1 gene, which encodes a choline transporter, as a crucial player in phloem development. In mutant plants, a fluorescent marker transported through the phloem failed to unload in the root tip, demonstrating defects in phloem transport. Further analysis revealed that the phloem strands are not continuous in the cher1 mutant, which also has short roots, abnormal roots hairs, and changes in the arrangement of the water-conducting xylem tissues.
CHER1 accumulates at one end of sieve element cells, collecting at the centre of the forming sieve plate. Examination with serial block-face scanning electron microscopy showed that mutant plants have smaller sieve plates with fewer, structurally-altered pores, inhibiting long-distance transport via the phloem. "Control of choline transport is essential to form continuously connected phloem with proper sieve plates, but we still have to uncover the exact cellular processes involved," says Helariutta.
|Contact: Yrjö Helariutta|
University of Helsinki