Rice phloem thioredoxin h has the capacity to mediate its own cell-to-cell transport through plasmodesmata

Planta. 1998 May;205(1):12-22. doi: 10.1007/s004250050291.


Rice (Oryza sativa L.) phloem sieve tubes contain RPP13-1, a thioredoxin h protein that moves around the plant via the translocation stream. Such phloem-mobile proteins are thought to be synthesized in the companion cells prior to being transferred, through plasmodesmata, to the enucleate sieve-tube members. In this study, in-situ hybridization experiments confirmed that expression of RPP13-1 is restricted to companion cells within the mature phloem. To test the hypothesis that RPP13-1 enters the sieve tube, via plasmodesmata, recombinant RPP13-1 was expressed in Escherichia coli, extracted, purified and fluorescently labeled with fluorescein isothiocyanate (FITC) for use in microinjection experiments into tobacco (Nicotiana tabacum L.) mesophyll cells. The FITC-RPP13-1 moved from the injected cell into surrounding cells, whereas the E. coli thioredoxin, an evolutionary homolog of RPP13-1, when similarly labeled and injected, failed to move in this same experimental system. In addition, co-injection of RPP13-1 and FITC-dextrans established that RPP13-1 can induce an increase in plasmodesmal size exclusion limit to a value greater than 9.4 but less than 20 kDa. Nine mutant forms of RPP13-1 were constructed and tested for their capacity to move from cell to cell; two such mutants were found to be incapable of movement. Crystal-structure prediction studies were performed on wild-type and mutant RPP13-1 to identify the location of structural motifs required for protein trafficking through plasmodesmata. These studies are discussed with respect to plasmodesmal-mediated transport of macromolecules within the companion cell-sieve tube complex.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Biological Transport
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Oryza / metabolism*
  • Plants, Toxic
  • Protein Conformation
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Sequence Homology, Amino Acid
  • Thioredoxin h
  • Thioredoxins / chemistry
  • Thioredoxins / genetics
  • Thioredoxins / metabolism*
  • Tobacco / genetics


  • RNA, Messenger
  • Thioredoxin h
  • Thioredoxins