C hlamydomonas NZF 1, a tandem‐repeated zinc finger factor involved in nitrate signalling by controlling the regulatory gene NIT 2

The C hlamydomonas reinhardtii   NIT 2 gene plays a central role in nitrate assimilation, thus, nit2 mutants are not able to sense or to use nitrate for growth. NIT 2 protein is an RWP‐RK ‐type transcriptional factor related to nodule inception ( N in, NLP ) proteins from plants. NIT 2 expression is down‐regulated in ammonium and up‐regulated under nitrogen deprivation. However, intracellular nitrate is required to activate NIT 2 for subsequent expression of NIA 1 and other nitrate assimilation genes. In this work, mutants defective in nitrate sensing have been studied. The identification of genomic regions affected allows proposing putative loci /genes for nitrate signalling in the alga. Among them, a C r NZF 1 ( N itrate   Z inc   F inger 1) that encodes a tandem zinc finger protein CCCH ‐type. In the nzf1 mutant, the expression of the regulatory gene NIT 2 is decreased and also that of nitrate assimilation genes. In this mutant, polyadenylated forms of NIT 2 with different lengths could be detected, whereas in the wild type there appeared preferentially the longest forms. Cr NZF 1 is proposed to regulate NIT 2 polyadenylation and thus nitrate signalling and nitrate‐dependent growth in the alga.