Cytokinin Promotes Jasmonic Acid Accumulation in the Control of Maize Leaf Growth

Plant organ growth results from the combined activity of cell division and cell expansion. The co-ordination of these two processes depends on the interplay between multiple hormones that determine the final organ size. Using the semidominant Hairy Sheath Frayed1 (Hsf1) maize mutant that hypersignals the perception of cytokinin (CK), we show that CK can reduce leaf size and growth rate by decreasing cell division. Linked to CK hypersignaling, the Hsf1 mutant has an increased jasmonic acid (JA) content, a hormone that can inhibit cell division. The treatment of wild-type seedlings with exogenous JA reduces maize leaf size and growth rate, while JA-deficient maize mutants have increased leaf size and growth rate. Expression analysis revealed the increased transcript accumulation of several JA pathway genes in the Hsf1 leaf growth zone. A transient treatment of growing wild-type maize shoots with exogenous CK also induced the expression of JA biosynthetic genes, although this effect was blocked by the co-treatment with cycloheximide. Together, our results suggest that CK can promote JA accumulation, possibly through the increased expression of specific JA pathway genes.

Automated summary

Plant organ growth is influenced by the interaction between cell division and cell expansion, which is regulated by multiple hormones. In this study, we found that the perception of cytokinin (CK) can reduce leaf size and growth rate by decreasing cell division. Furthermore, we demonstrated that the increased jasmonic acid (JA) content in the Hsf1 maize mutant, which hypersignals CK, inhibits cell division. Treatment with exogenous JA also decreased leaf size and growth rate in wild-type seedlings, while JA-deficient maize mutants exhibited increased leaf size and growth rate.