SAUR15 Connects Auxin Perception to Lateral and Adventitious Root Formation

Small Auxin Up RNA 56 (SAUR56) regulates heading date in rice

Heading date is a critical agronomic trait that determines crop yield. Although numerous genes associated with heading date have been identified in rice, the mechanisms involving Small Auxin Up RNA (SAUR) family have not been elucidated. In this study, the biological function of several SAUR genes was initially investigated using the CRISPR-Cas9 technology in the Japonica cultivar Zhonghua11 (ZH11) background. Further analysis revealed that the loss-of-function of OsSAUR56 affected heading date in both NLD (natural long-day) and ASD (artificial short-day). OsSAUR56 exhibited predominant expression in the anther, with its protein localized in both the cytoplasm and nucleus. OsSAUR56 regulated flowering time and heading date by modulating the expression of the clock gene OsGI, as well as two repressors Ghd7 and DTH8. Furthermore, haplotype-phenotype association analysis revealed a strong correlation between OsSAUR56 and heading date, suggesting its role in selection during the domestication of rice. In summary, these findings highlights the importance of OsSAUR56 in the regulation of heading date for further potential facilitating genetic engineering for flowering time during rice breeding.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01409-w.

Folate shapes plant root architecture by affecting auxin distribution

Folate (vitamin B9) is important for plant root development, but the mechanism is largely unknown. Here we characterized a root defective mutant, folb2, in Arabidopsis, which has severe developmental defects in the primary root. The root apical meristem of the folb2 mutant is impaired, and adventitious roots are frequently found at the root-hypocotyl junction. Positional cloning revealed that a 61-bp deletion is present in the predicted junction region of the promoter and the 5' untranslated region of AtFolB2, a gene encoding a dihydroneopterin aldolase that functions in folate biosynthesis. This mutation leads to a significant reduction in the transcript level of AtFolB2. Liquid chromatography-mass spectrometry analysis showed that the contents of the selected folate compounds were decreased in folb2. Arabidopsis AtFolB2 knockdown lines phenocopy the folb2 mutant. On the other hand, the application of exogenous 5-formyltetrahydrofolic acid could rescue the root phenotype of folb2, indicating that the root phenotype is indeed related to the folate level. Further analysis revealed that folate could promote rootward auxin transport through auxin transporters and that folate may affect particular auxin/indole-3-acetic acid proteins and auxin response factors. Our findings provide new insights into the important role of folic acid in shaping root structure.

Transcription Factor SmSPL2 Inhibits the Accumulation of Salvianolic Acid B and Influences Root Architecture

The SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL) transcription factor play vital roles in plant growth and development. Although 15 SPL family genes have been recognized in the model medical plant Salvia miltiorrhiza Bunge, most of them have not been functionally characterized to date. Here, we performed a careful characterization of SmSPL2, which was expressed in almost all tissues of S. miltiorrhiza and had the highest transcriptional level in the calyx. Meanwhile, SmSPL2 has strong transcriptional activation activity and resides in the nucleus. We obtained overexpression lines of SmSPL2 and rSmSPL2 (miR156-resistant SmSPL2). Morphological changes in roots, including longer length, fewer adventitious roots, decreased lateral root density, and increased fresh weight, were observed in all of these transgenic lines. Two rSmSPL2-overexpressed lines were subjected to transcriptome analysis. Overexpression of rSmSPL2 changed root architectures by inhibiting biosynthesis and signal transduction of auxin, while triggering that of cytokinin. The salvianolic acid B (SalB) concentration was significantly decreased in rSmSPL2-overexpressed lines. Further analysis revealed that SmSPL2 binds directly to the promoters of Sm4CL9, SmTAT1, and SmPAL1 and inhibits their expression. In conclusion, SmSPL2 is a potential gene that efficiently manipulate both root architecture and SalB concentration in S. miltiorrhiza.

SAUR15 interaction with BRI1 activates plasma membrane H+-ATPase to promote organ development of Arabidopsis

Brassinosteroids (BRs) are an important group of plant steroid hormones that regulate growth and development. Several members of the SMALL AUXIN UP RNA (SAUR) family have roles in BR-regulated hypocotyl elongation and root growth. However, the mechanisms are unclear. Here, we show in Arabidopsis (Arabidopsis thaliana) that SAUR15 interacts with cell surface receptor-like kinase BRASSINOSTEROID-INSENSITIVE 1 (BRI1) in BR-treated plants, resulting in enhanced BRI1 phosphorylation status and recruitment of the co-receptor BRI1-ASSOCIATED RECEPTOR KINASE 1. Genetic and phenotypic assays indicated that the SAUR15 effect on BRI1 can be uncoupled from BRASSINOSTEROID INSENSITIVE 2 activity. Instead, we show that SAUR15 promotes BRI1 direct activation of plasma membrane H+-ATPase (PM H+-ATPase) via phosphorylation. Consequently, SAUR15-BRI1-PM H+-ATPase acts as a direct, PM-based mode of BR signaling that drives cell expansion to promote the growth and development of various organs. These data define an alternate mode of BR signaling in plants.

Transcriptomic Insight into Viviparous Growth in Water Lily

Water lily is an important ornamental flower plant which is capable of viviparous plantlet development. But no study has been reported on the molecular basis of viviparity in water lily. Hence, we performed a comparative transcriptome study between viviparous water lily Nymphaea micrantha and a nonviviparous species Nymphaea colorata at four developmental stages. The higher expression of highly conserved AUX/IAA, ARF, GH3, and SAUR gene families in N. micrantha compared to N. colorata is predicted to have a major impact on the development and evolution of viviparity in water lily. Likewise, differential regulation of hormone signaling, brassinosteroid, photosynthesis, and energy-related pathways in the two species provide clues of their involvement in viviparity phenomenon. This study revealed the complex mechanism of viviparity trait in water lily. The transcriptomic signatures identified are important basis for future breeding and research of viviparity in water lily and other plant species.

Molecular Bases for the Regulation of Adventitious Root Generation in Plants

The formation of adventitious roots (ARs) is an ecologically and economically important developmental process in plants. The evolution of AR systems is an important way for plants to cope with various environmental stresses. This review focuses on identified genes that have known to regulate the induction and initiation of ARs and offers an analysis of this process at the molecular level. The critical genes involved in adventitious rooting are the auxin signaling-responsive genes, including the AUXIN RESPONSE FACTOR (ARF) and the LATERAL ORGAN BOUNDARIES-DOMAIN (LOB) gene families, and genes associated with auxin transport and homeostasis, the quiescent center (QC) maintenance, and the root apical meristem (RAM) initiation. Several genes involved in cell wall modulation are also known to be involved in the regulation of adventitious rooting. Furthermore, the molecular processes that play roles in the ethylene, cytokinin, and jasmonic acid signaling pathways and their crosstalk modulate the generation of ARs. The crosstalk and interaction among many molecular processes generates complex networks that regulate AR generation.