Abstract
Zn deficiency is the most common micronutrient deficit in rice but also
a widespread industrial pollutant. It is unclear how rice responds to Zn
depletion or excess, and which signaling molecules link the affected
physiological processes. We therefore compared the physiological,
transcriptomic and biochemical properties of rice plants subjected to Zn
starvation or excess at early and later treatment stages. Both forms of
Zn stress inhibited root and shoot growth. Several divalent cations (Fe,
Cu, Ca, Mn and Mg) accumulated in Zn-depleted shoots, possibly due to
the increased synthesis and activity of promiscuous Zn transporters and
chelators. Gene Ontology enrichment analysis of 970 differentially
expressed genes revealed overrepresentation of ion and oligopeptide
transport, antioxidative defense and secondary metabolism. The
expression of genes encoding Fe/Ca-binding peroxidases was activated
after 3 days of Zn starvation, boosting the activity of ascorbate
peroxidase and thus scavenging H2O2 more
effectively to prevent leaf chlorosis. Conversely, excess Zn triggered
the expression of genes encoding Mg-binding proteins (OsCPS2/4
and OsKSL4/7) required for antimicrobial diterpenoid
biosynthesis. We demonstrated the key components of crosstalk between Zn
and other divalent cations under Zn stress conditions, leading to the
regulation of gene expression and corresponding biochemical and
physiological processes.