NTZIP antisense plants show reduced chlorophyll levels.

We have isolated and characterized a new photosynthetic tissue-specific gene NTZIP (Nicotiana tabacum leucine zipper) from tobacco (N. tabacum). Its deduced amino acid sequence has two highly conserved regions, leucine zipper and [EX(n)DEXRH](2) motifs, which are related to the gene's biochemical functions. NTZIP was expressed in leaves and stems, but was not detected in roots or flowers, suggesting that its physiological functions might be associated with photosynthesis. Northern blot analysis showed that NTZIP mRNA accumulation was induced by light signals, increased greatly under low temperatures and was repressed by strong light illumination. Furthermore, a number of homologs of NTZIP were isolated from cucumber (Cucumis sativus), rape (Brassica napus), clover (Trifolium repens), willow (Salix babylonica), rosebush (Rusa dovurica), wheat (Triticum aestivum) and spinach (Spinacia oleracea), proving the ubiquitous existence of the NTZIP-like genes in higher plants. Transgenic tobaccos constitutively expressing antisense RNA to NTZIP displayed chlorosis and a lack of ability to turn green even under normal growth conditions. The chlorophyll deficiency was further confirmed by chlorophyll content determination and gas exchange analysis. Based on these observations, we propose that NTZIP may be involved in chlorophyll biosynthesis, and might define a novel family of evolutionarily conserved proteins with its homologs in other plant species.