| Strigolactone (s) (SL) is a new type of plant hormone identified recently.It can stimulate the germination of parasitic plants as well as play roles in the regulation of plant growth and development such as eliciting to establish a symbiotic growthbetween plants andarbuscular mycorrhizal fungi, alteration of plant upper-part architecture by inhibiting shoot-branching, effect on plant root growth. Regarding the movementof SLin theplant, only a protein called PhPDRl from a witchweed or Strigahas been demonstrated for the transport of SL at a molecular and physiological level.In this work, the involvement of a strigolactone tansporter homolog OsPDR8 from ricein root hair growth and in the response of the plant to nitrogen and phosphorus nutrient has been investigated. Major results are summarized as below:It has been found that root hair growth of rice became more sensitive to an externally applied synthetic strigolactone (GR24) when a putative strigolactone transporter OsPDR8 was mutated by a T-DNA insertion. Compared with the wild-type and strigolactone synthesis mutant d10, exogenous strigolactone (GR24)at a concentration of 1×10-8M wasfound to more significantly promote the growth of root hairs ofospdr8 mutant line, whereas the root hair elongation of the mutant was greatly inhibited as the concentration of GR24 reached 3×10-6M.The expression of OsPDR8in roots and shoots was induced by strigolactone GR24. The transcripts of OsPDR8 in the shoots were obviously increased after 30 min GR24-treatment; the highest expression of OsPDR8cccurred after 60 min exposure of plants to GR24. Promoter (ProOsPDR8) activity study of OsPDR8 showed that signals derived from GFP expression driven by the ProOsPDR8could be well detected after 30 min GR24-presence and were then increased after 60 min GR24-treatment, again emphasizing our suggestion that OsPDR8 was transcriptionally up-regulated by GR24 as well as that the sequence of OsPDR8 promoter should/might contain a stigolactone-(GR24) responsivesis-element (s).Moreover, the transcriptional expression of OsPDR8was found to be inducedby the deficiency of nitrogen or phosphorusin rice. The amount ofOsPDR8mRNA in roots was markedlyelevated when rice was starved of nitrogen for 3 daysas compared with control supplied with normal N-regime, but was dramatically decreased when resupplied with ammonium or nitrate to the N-starved rice. Similarly, P-starvation of the plants also induced the expression of OsPDR8 in the roots (but this was not observed in the one-day P-staved plants compared with the controlsupplied normally with P),re-provision with P to P-starved rice led to a decline of OsPDR8mRNA to a level of the control. These results propose that OsPDR8 being a putative SL-transporter might be involved in SL-regulated plant N-and P-nutrient physiology.A functional study using heterologousgene-expressionsystem revealed that Arabidopsis lines with the overexpression of rice Os.PDR8exhibiteda better tolerance to a higher GR24(i.e.10-20μM)growth condition as compared with non-transgenic plants, thusrelievingpossibly the plants from higher SL-induced stress tosome extent.Taken together, rice OsPDR8 might serve as an exporter for the movement of strigolactone, similar to its homologue PhPDR1. OsPDR8-transported substrate(s)like SL might interact with other plant hormonesto alter the concentration of auxin in epidermal cells, thus affecting root hair growth as well as regulating plant growth in response to the variation of N-or P-nutritional status. |
