Abstract
A class 1 non-symbiotic hemoglobin family gene, SoHb, was isolated from spinach. qRT-PCR showed that SoHb was induced by excess nitrate, polyethylene glycol, NaCl, H2O2, and salicylic acid. Besides, SoHb was strongly induced by application of nitric oxide (NO) donor, while was suppressed by NO scavenger, nitrate reductase inhibitor, and nitric oxide synthase inhibitor. Overexpression of SoHb in Arabidopsis resulted in decreased NO level and sensitivity to nitrate stress, as shown by reduced root length, fresh weight, the maximum photosystem II quantum ratio of variable to maximum fluorescence (Fv/Fm), and higher malondialdehyde contents. The activities and gene transcription of superoxide dioxidase, and catalase decreased under nitrate stress. Expression levels of RD22, RD29A, DREB2A, and P5CS1 decreased after nitrate treatment in SoHb-overexpressing plants, while increased in the WT plants. Moreover, SoHb-overexpressing plants showed decreased tolerance to NaCl and osmotic stress. In addition, the SoHb-overexpression lines showed earlier flower by regulating the expression of SOC, GI and FLC genes. Our results indicated that the decreasing NO content in Arabidopsis by overexpressing SoHb might be responsible for lowered tolerance to nitrate and other abiotic stresses.
Highlights
Hemoglobins (Hbs) are ubiquitous proteins found in all kingdoms of life[5]
We identified a gene encoding Hb in spinach root, which was designated as SoHb
GhHb1 expression was induced by salicylic acid (SA), H2O2 and NO13
Summary
Hemoglobins (Hbs) are ubiquitous proteins found in all kingdoms of life[5]. In plants, three types of hemoglobins exist: symbiotic, non-symbiotic, and truncated hemoglobins. NsHb1 is involved in various biotic and abiotic stress responses. Studies of transgenic Arabidopsis and alfalfa root cultures overexpressing nsHb1 genes suggest that nsHb1 may be involved in NO-mediated pathways of hypoxic or early-growth states[28,29]. Spinach (Spinacia oleracea L.) is one of the most popular leafy vegetables grown in Chinese greenhouses, in the Dianchi River division of Yunnan province. It is an excellent source of dietary vitamins and minerals such as calcium and magnesium. Expression of the SoHb gene was analyzed by real-time quantitative RT-PCR (qRT-PCR) in spinach grown under nitrate or other abiotic stresses. Ectopic expression in Arabidopsis conferred decreased tolerance to nitrate and other abiotic stresses
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