Leaf morphogenesis is governed by a tightly integrated regulatory network centered on auxin, which operates through a sequential axis of synthesis, transport, and signal transduction. This review elucidates how pivotal molecular hubs previously identified in this regulatory network, including biosynthetic enzymes, polar transporters, and auxin response factors, interconnect through dynamic feedback mechanisms to orchestrate leaf initiation, polarity establishment, and the determination of its final size and shape. Notably, recent breakthroughs are transforming the field: the re-evaluation of established pathways like indole-3-acetaldoxime (IAOx), whose direct contribution to auxin pools is under scrutiny, hinting at the existence of undiscovered enzymes or alternative metabolic branches and the paradigm-shifting discovery that cAMP functions as a second messenger produced by Transport Inhibitor Resistant 1/Auxin signaling F-box (TIR1/AFB) receptors, which directly activates Auxin Response Factor (ARF)-mediated transcription. These foundational mechanistic insights provide the critical groundwork for application. Key network nodes—such as PIN-FORMED (PIN) transporters and YUCCA (YUC) flavin-containing monooxygenases—are now validated targets for crop improvement. Consequently, the elucidated network serves as a blueprint for rationally designing crop architecture.

Identifying key genes involved in Cadmium (Cd) response pathways in plants and developing low-Cd-accumulating cultivars may be the most effective and eco-friendly strategy to tackle the problem of Cd pollution in crops. In our previous study, Stressseventy subfamily A 4 (SSA4) was identified to be associated with Cd tolerance in yeast. Here, we investigated the mechanism of SSA4 in regulating Cd tolerance in yeast. ScSSA4 binds to POre Membrane 34 (POM34), a key component of nuclear pore complex (NPC), and translocates from the cytoplasm to the nucleus, where it regulates the expression of its downstream gene, Viable in a Hal3 Sit4 background 1 (VHS1), resulting in reduced Cd accumulation in yeast cells. Additionally, we identified a Chinese cabbage SSA4 gene, BrSSA4c, which could enhance the Cd tolerance in Chinese cabbage. This study offers new insights into the regulatory mechanisms of Cd tolerance in yeast, a model organism, and paves the way for the genetic enhancement of Cd tolerance in Chinese cabbage.

Cysteine-rich transmembrane module (CYSTM) peptides are ubiquitous in eukaryotes and primarily involved in stress responses and defense mechanisms. To date