Sulfur deprivation-induced expression of THB1, a Chlamydomonas reinhardtii truncated hemoglobin,is mediated by nitrate reductase-dependent NO production

摘要

During sulfur (S) deprivation, Chlamydomonas reinhardtii mediates a suite ofspecific responses to efficiently acquire S from various sources and remodel primarymetabolism. Although the truncated hemoglobin 1 (THB1)-dependent regulation ofa subset of S limitation-responsive genes has been elucidated, the mechanism throughwhich THB1 transcription is triggered in S-deprived cells is not known. Here, we showthat signaling proteins and regulators associated with S deprivation specific responsesdid not control THB1 expression. Following S depletion, rapid increase in nitriteconcentrations is essential for THB1 upregulation. These changes are consistent withNO accumulation. Increased nitrite, NO and THB1 mRNA levels were not observedin mutant cells without diaphorase-NR activity. Our findings suggest that nitratereductase - nitric oxide-forming nitrite reductase system plays a positive role in THB1transcription via generation of NO from nitrite in S-starved cells. NR-dependent NOproduction may be regarded as an early trigger, which contributes to Chlamydomonasadaptability to nutrient stresses.