EFFECTS OF VACUOLAR TRANSPORTER CHAPERONE 1 DISRUPTION ON PHOSPHORUS STRESS RESPONSE NETWORK IN CHLAMYDOMONAS REINHARDTII

Phosphorus (P) stress response network and transport has been
studied in microalgae. However, less is known about the interactions
between polyphosphate (polyP) biosynthesis and P stress response
network. Also, knowledge about polyP metabolism in microalgae remains
limited. In this study, the molecular mechanisms of polyP biosynthesis
and its link with P stress response regulation and phosphate (Pi) transport
were investigated in Chlamydomonas reinhardtii using a mutant defective
in the vacuolar transporter chaperone 1 gene (VTC1). The presence of
polyP was abundant in the C. reinhardtii VTC1 rescue strains when Pi
was copious, whereas polyP was degraded when P was depleted in the
medium. Also, deletion of VTC1 severely repressed the expression (20-
fold compared to the expression in VTC1 rescue) of Phosphorus Stress
Regulator 1 (PSR1) as well as Phosphate Transporter Type B2 (PTB2)
and PTB4, suggesting that defects of VTC1 may perturb the P stress
response through repression of PSR1 expression. Moreover, differentiated
expressions of type A (acidic phosphate transporters) and type B (alkaline
phosphate transporters) are observed in response to P deprivation. These
EFFECTS OF VACUOLAR TRANSPORTER CHAPERONE 1 DISRUPTION90
data suggest that PTBs in C. reinhardtii, grown in neutral to slight basic
medium pH conditions, may be the primary Pi transporters under P
deprivation and they are controlled by PSR1 which is may be regulated by
polyP molecules. Thus, manipulation of polyP biosynthesis under P stress
condition may be a promising strategy for agriculture in alkaline soil to
face and tolerate P deprivation stress.