Sulfite Oxidase is Essential for Timely Germination of Maize Seeds upon Sulfite Exposure

Abstract

Acid rain adversely affects maize seed germination by sulfite toxicity. Unfortunately, the molecular mechanisms underlying seed germination inhibition by sulfite in maize are largely unknown. Previously, the involvement of sulfite oxidase (SO) in sulfite detoxification in model plants was characterized. Here, we characterized Zea mays SO (ZmSO) in transgenic maize to investigate its role during seed germination upon sulfite exposure. ZmSO was responsive to sulfite stress at the transcriptional level during germination of maize seeds. Unlike the null mutant atso-1, ZmSO-overexpressing transgenic Arabidopsis plants were tolerant to SO2 stress and could effectively rescue the susceptible phenotype of atso-1. Silencing of ZmSO could lead to seed germination delay upon sulfite exposure, but not under normal conditions; interestingly, expressions of several seed germination-related genes encoding hydrolytic enzymes such as α-amylase, β-amylase, and glucosidase were reduced markedly in germinating seeds of ZmSO-compromised lines. This indicates that embryonic SO might alleviate the inhibitory effect of toxic sulfite by sulfite oxidation and the modulation of several hydrolytic enzymes during seed germination. Collectively, these data demonstrate that embryonic SO could be essential for timely seed germination upon sulfite exposure in maize. ZmSO might be a promising target for genetic improvement of crops tolerant to acid rain in molecular breeding programs.