Phytohormones are natural chemical messengers that play critical roles in the regulation of plant growth and development as well as responses to biotic and abiotic stress factors, maintaining plant homeostasis, and allowing adaptation to environmental changes. The discovery of a new class of phytohormones, the brassinosteroids (BRs), almost 40 years ago opened a new era for the studies of plant growth and development and introduced new perspectives in the regulation of agronomic traits through their use in agriculture. BRs are a group of hormones with significant growth regulatory activity that act independently and in conjunction with other phytohormones to control different BR-regulated activities. Genetic and molecular research has increased our understanding of how BRs and their cross-talk with other phytohormones control several physiological and developmental processes. The present article provides an overview of BRs’ discovery as well as recent findings on their interactions with other phytohormones at the transcriptional and post-transcriptional levels, in addition to clarifying how their network works to modulate plant growth, development, and responses to biotic and abiotic stresses.

How eukaryotic cells assess and maintain sizes specific for their species and cell type remains unclear. We show that in the Arabidopsis shoot stem cell niche, cell size variability caused by asymmetric divisions is corrected by adjusting the growth period before DNA synthesis. KIP-related protein 4 (KRP4) inhibits progression to DNA synthesis and associates with mitotic chromosomes. The F BOX-LIKE 17 (FBL17) protein removes excess KRP4. Consequently, daughter cells are born with comparable amounts of KRP4. Inhibitor dilution models predicted that KRP4 inherited through chromatin would robustly regulate size, whereas inheritance of excess free KRP4 would disrupt size homeostasis, as confirmed by mutant analyses. We propose that a cell cycle regulator, stabilized by association with mitotic chromosomes, reads DNA content as a cell size–independent scale.

The diversity and environmental plasticity of plant growth results from variations of repetitive modules, such as the basic shoot units made of a leaf, axillary bud, and internode. Internode elongation is regulated both developmentally and in response to environmental conditions, such as light quality, but the integration of internal and environmental signals is poorly understood. Here, we show that the compressed rosette growth habit ofArabidopsisis maintained by the convergent activities of the organ boundary geneARABIDOPSIS THALIANA HOMEOBOX GENE 1(ATH1) and of the gibberellin-signalingDELLAgenes. Combined loss ofATH1andDELLAfunction activated stem development during the vegetative phase and changed the growth habit from rosette to caulescent. Chromatin immunoprecipitation high-throughput sequencing and genetic analysis indicated thatATH1and theDELLAgeneREPRESSOR OF GA1-3(RGA) converge on the regulation of light responses, including thePHYTOCHROME INTERACTING FACTORS(PIF) pathway, and showed that theATH1input is mediated in part by direct activation ofBLADE ON PETIOLE(BOP1andBOP2) genes, whose products destabilize PIF proteins. We conclude that an organ-patterning gene converges with hormone signaling to spatially restrict environmental responses and establish a widespread type of plant architecture.

Modulation of gibberellic acid signaling through ScGAI regulates culm development including change in phytomer production and source–sink regulation in sugarcane.