OsMYB84,a transcriptional regulator of OsCOPT2 and OsHMA5,modulates copper uptake and transport and yield production in rice

Transcription factors regulating crop uptake and translocation of the micronutrient Cu have not been identified.We isolated a novel R2R3-MYB transcription factor,OsMYB84,and showed that it was a positive regulator involved in uptake and transport of Cu via activation of OsCOPT2 and OsHMA expression.OsMYB84 was highly expressed in roots and anthers and induced by Cu.Overexpression of OsMYB84 promoted uptake and root-to-shoot translocation of Cu in rice,facilitated Cu distribution into grain and increased grain yield.In contrast,mutation of OsMYB84 reduced Cu concentration in xylem sap.OsMYB84 bound to the promoter region of OsCOPT2 and OsHMA5 and upregulated their expression.OsCOPT2 mutants showed reduced uptake of Cu and OsHMA5 overexpression lines showed increased root-to-shoot translocation of Cu.

Induction of jasmonic acid biosynthetic genes inhibits Arabidopsis growth in response to low boron

The essential micronutrient boron(B) has key roles in cell wall integrity and B deficiency inhibits plant growth. The role of jasmonic acid(JA) in plant growth inhibition under B deficiency remains unclear. Here,we report that low B elevates JA biosynthesis in Arabidopsis thaliana by inducing the expression of JA biosynthesis genes. Treatment with JA inhibited plant growth and, a JA biosynthesis inhibitor enhanced plant growth, indicating that the JA induced by B deficiency affects plant growth. Furthermore,examination of the JA signaling mutants jasmonate resistant1, coronatine insensitive1-2, and myc2 showed that JA signaling negatively regulates plant growth under B deficiency. We identified a low-B responsive transcription factor, ERF018, and used yeast one-hybrid assays and transient activation assays in Nicotiana benthamiana leaf cells to demonstrate that ERF018 activates the expression of JA biosynthesis genes. ERF018 overexpression(OE)lines displayed stunted growth and up-regulation of JA biosynthesis genes under normal B conditions,compared to Col-0 and the difference between ERF018 OE lines and Col-0 diminished under low B.These results suggest that ERF018 enhances JA biosynthesis and thus negatively regulates plant growth. Taken together, our results highlight the importance of JA in the effect of low B on plant growth.

Brassinosteroid signaling regulates phosphate starvation-induced malate secretion in plants

Inorganic phosphate(Pi)is often limited in soils due to precipitation with iron(Fe)and aluminum(Al).To scavenge heterogeneously distributed phosphorus(P)resources,plants have evolved a local Pi signaling pathway that induces malate secretion to solubilize the occluded Fe-P or Al-P oxides.In this study,we show that Pi limitation impaired brassinosteroid signaling and downregulated BRASSINAZOLE-RESISTANT 1(BZR1)expression in Arabidopsis thaliana.Exogenous 2,4-epibrassinolide treatment or constitutive activation of BZR1(in the bzr1-D mutant)significantly reduced primary root growth inhibition under Pi-starvation conditions by downregulating ALUMINUM-ACTIVATED MALATE TRANSPORTER 1(ALMT1)expression and malate secretion.Furthermore,At BZR1 competitively suppressed the activator effect of SENSITIVITY TO PROTON RHIZOTOXICITY 1(STOP1)on ALMT1 expression and malate secretion in Nicotiana benthamiana leaves and Arabidopsis.The ratio of nuclear-localized STOP1 and BZR1 determined ALMT1 expression and malate secretion in Arabidopsis.In addition,BZR1-inhibited malate secretion is conserved in rice(Oryza sativa).Our findings provide insight into plant mechanisms for optimizing the secretion of malate,an important carbon resource,to adapt to Pi-deficiency stress.