Grain size is an important agronomic trait, but our knowledge about grain size determination in crops is still limited. Endoplasmic reticulum (ER)–associated degradation (ERAD) is a special ubiquitin proteasome system that is involved in degrading misfolded or incompletely folded proteins in the ER. Here, we report that SMALL GRAIN 3 (SMG3) and DECREASED GRAIN SIZE 1 (DGS1), an ERAD-related E2–E3 enzyme pair, regulate grain size and weight through the brassinosteroid (BR) signaling pathway in rice (Oryza sativa). SMG3 encodes a homolog of Arabidopsis (Arabidopsis thaliana) UBIQUITIN CONJUGATING ENZYME 32, which is a conserved ERAD-associated E2 ubiquitin conjugating enzyme. SMG3 interacts with another grain size regulator, DGS1. Loss of function of SMG3 or DGS1 results in small grains, while overexpression of SMG3 or DGS1 leads to long grains. Further analyses showed that DGS1 is an active E3 ubiquitin ligase and colocates with SMG3 in the ER. SMG3 and DGS1 are involved in BR signaling. DGS1 ubiquitinates the BR receptor BRASSINOSTEROID INSENSITIVE 1 (BRI1) and affects its accumulation. Genetic analysis suggests that SMG3, DGS1, and BRI1 act together to regulate grain size and weight. In summary, our findings identify an ERAD-related E2–E3 pair that regulates grain size and weight, which gives insight into the function of ERAD in grain size control and BR signaling.

Leaf size influences plant development and biomass and is also an important agricultural trait in Brassica crops, in which leaves are the main organ produced for consumption. Leaf size is determined by the coordinated regulation of cell proliferation and cell expansion during leaf development, and these processes are strictly controlled by various integrated signals from the intrinsic regulatory network and the growth environment. Understanding the molecular mechanism of leaf size control is a prerequisite for molecular breeding for crop improvement purposes. Although research on leaf size control is just beginning in Brassica, recent studies have identified several genes and QTLs that are important in leaf size regulation. These genes have been proposed to influence leaf growth through different pathways and mechanisms, including phytohormone biosynthesis and signaling, transcription regulation, small RNAs, and others. In this review, we summarize the current findings regarding the genetic regulators of leaf size in Brassica and discuss future prospects for this research.

Grain size, a main component of grain yield, is regulated by a complex network. The mitogen-activated protein kinase (MAPK) cascade participates in multiple signaling pathways to regulate various biological processes. Recent studies indicate that MAPK signaling plays key roles in regulating grain size. For instance, OsERECTA1(OsER1)–OsMKKK10–OsMKK4–OsMPK6 signaling regulates grain size and grain number per panicle. Grain size is also affected by the OsMKKK70–OsMKK4–OsMPK6 module, which functions upstream of OsWRKY53. In addition, MITOGEN-ACTIVATED PROTEIN KINASE PHOSPHATASE1 (OsMKP1), the GSK3/SHAGGY-like kinase GSK2, and the Rho-family GTPase OsRac1 controls grain size in rice by modulating MAPK signaling. Here, we discuss recent findings on the importance of MAPK signaling in rice grain-size control and examine mechanisms by which MAPK signaling coordinates grain size, grain number and stress responses.

The DA1/DAR family genes have been shown to play important roles in regulating organ size and plant biomass in the model plant Arabidopsis and several crops. However, this family has not been characterized in Brassica rapa (B. rapa). In this study, we identified 17 DA1&DAR genes from B. rapa. Phylogenetic analysis indicated that these genes are classified into four groups. Structural and motif analysis of BrDA1&DARs discovered that the genes within the same group have similar exon-intron structures and share an equal number of conserved motifs except for BrDAR6.3 from group IV, which contains two conserved motifs. Cis-regulatory elements identified four phytohormones (Salicylic acid, Abscisic acid, Gibberellin, and auxin) and three major abiotic (Light, Low temperature, and drought) responsive elements. Further, six br-miRNAs named br-miR164a, br-miR164b, br-miR164c, br-miR164d, br-miRN360, and br-miRN366 were found which target BrDAR6.1, BrDA1.4, and BrDA1.5. BrDA1&DAR genes were highly expressed in stem, root, silique, flower, leaf, and callus tissues. Moreover, qRT-PCR analyses indicated that some of these genes were responsive to abiotic stresses or phytohormone treatments. Our findings provide a foundation for further genetic and physiological studies of BrDA1&DARs in B. rapa.

The dynamic regulation of histone methylation is a key mechanism for epigenetic regulation of gene expression. As histone demethylases dependent on divalent iron ions and α-ketoglutarate, the JmjC family plays an important role in plant life activities. Fifty JmjC domain-containing proteins in Arabidopsis thaliana (21) and Brassica rapa (29) are divided into seven distinct groups, with each group endowed with specific functions due to unique structural domains. Some members achieve functional specificity by recognizing specific DNA motifs or interacting with transcription factors, and others exhibit special functional modes due to mutations in their binding sites. By targeting specific genes (such as FLC, FT, WRKY family, PR genes, etc.), they regulate growth and development processes, as well as responses to multiple biotic and abiotic stresses. Focusing on inter-species divergence of Arabidopsis and Brassica, this review summarized JmjC proteins’ structural classification, substrate specificity, and mechanisms, providing a basis for dissecting plant epigenetic networks and guiding Brassica crop breeding desired bolting traits (early or late bolting), high stress resistance and so on.