Abstract
WRKYs are transcriptional factors involved in stress tolerance and development of plants. In the present study, we characterized OsWRKY28, a group IIa WRKY gene, in rice, because its expression was found to be upregulated by arsenate exposure in previous transcriptomic studies. Subcellular localization using YFP–OsWRKY28 fusion protein showed that the protein was localized in the nuclei. Transgenic rice plants expressing pOsWRKY28::GUS suggested that the gene was expressed in various tissues in the whole plant, with a strong expression in the root tips, lateral roots and reproductive organs. The expression of OsWRKY28 was markedly induced by arsenate and other oxidative stresses. In a hydroponic experiment, loss-of-function mutation in OsWRKY28 resulted in lower accumulation of arsenate and phosphate concentration in the shoots. The mutants showed altered root system architecture, with fewer lateral roots and shorter total root length than wild-type plants. In a soil pot experiment, the mutants produced lower grain yield than wild-type because of reduced fertility and smaller effective tiller numbers. Transcriptomic profiling using RNA-seq showed altered expression in the mutant of genes involved in the biosynthesis of phytohormones, especially jasmonic acid (JA). Exogenous JA treatments mimicked the phenotypes of the oswrky28 mutants with inhibited root elongation and decreased arsenate/phosphate translocation. Our results suggested that OsWRKY28 affected arsenate/phosphate accumulation, root development at the seedling stage and fertility at the reproductive stage possibly by influencing homeostasis of JA or other phytohormones.
Highlights
Inorganic arsenic (As) is a non-threshold carcinogen
We further investigated the possible involvement of the plant hormone, jasmonic acid (JA), in the regulation of As(V) uptake by OsWRKY28
OsWRKY28 has been reported to be involved in the innate immune responses to the infection of rice blast fungus (Peng et al, 2010; Delteil et al, 2012; Chujo et al, 2013)
Summary
Inorganic arsenic (As) is a non-threshold carcinogen. Humans are exposed to inorganic As mainly through drinking water and food. Arsenic contamination in paddy soils is a common problem worldwide due to mining and smelting, irrigation of As-laden groundwater, and uses of As-containing agrochemicals. Contaminated paddy soils can result in elevated accumulation of As in rice grain and pose a significant risk to the health of people consuming rice as their staple food (Meharg, 2004; Zhao et al, 2010; Banerjee et al, 2013). At high levels of contamination, As can cause phytotoxicity and substantial yield losses (Panaullah et al, 2009; Khan et al, 2010; Huhmann et al, 2017)
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