Wheat TaSPL8 Modulates Leaf Angle Through Auxin and Brassinosteroid Signaling

Abstract

In grass crops, leaf angle is determined by development of the lamina joint, the tissue connecting the leaf blade and sheath, and is closely related to crop architecture and yield. In this study, we identified a mutant generated by fast neutron radiation that exhibited an erect leaf phenotype caused by defects in lamina joint development. Map-based cloning revealed that the gene TaSPL8, encoding a SQUAMOSA PROMOTER BINDING-LIKE (SPL) protein, is deleted in this mutant. TaSPL8 knockout mutants exhibit erect leaves due to loss of the lamina joint, compact architecture, and increased spike number especially in high planting density, suggesting similarity with its LIGULESS1 homologs in maize (Zea mays) and rice (Oryza sativa). Hence, LG1 could be a robust target for plant architecture improvement in grass species. Common wheat (Triticum aestivum, 2n 5 63 5 42; BBAADD) is an allohexaploid containing A, B, and D subgenomes and the homeologous gene of TaSPL8 from the D subgenome contributes to the length of the lamina joint to a greater extent than that from the A and B subgenomes. Comparison of the transcriptome between the Taspl8 mutant and the wild type revealed that TaSPL8 is involved in the activation of genes related to auxin and brassinosteroid pathways and cell elongation. TaSPL8 binds to the promoters of the AUXIN RESPONSE FACTOR gene and of the brassinosteroid biogenesis gene CYP90D2 and activates their expression. These results indicate that TaSPL8 might regulate lamina joint development through auxin signaling and the brassinosteroid biosynthesis pathway.

Exploring the Brassinosteroid Signaling in Monocots Reveals Novel Components of the Pathway and Implications for Plant Breeding

“…Consequently, it regulates leaf inclination in wheat (Figure 2). Therefore, it was concluded that the TaSPL8 gene may be regarded as a potential target for modulation of the plant architecture in cereals [8].…”

“…Leaf angle is one of the key parameters determining cereal crop architecture and yield [7]. Thus, breeding cereals for more erect leaves is a strategy for the crop productivity improvement [8]. Brassinosteroids (BRs) play a prominent role in hormonal crosstalk which regulates this parameter in cereals [7,[9][10][11].…”

COMPOSITUM 1 (COM1) contributes to the architectural simplification of barley inflorescence via meristem identity signals

“…Among significantly downregulated genes across all three stages ( Fig. 5B ), we detected one SQUAMOSA PROMOTER-BINDING-LIKE 8 gene ( SPL8 , HORVU2Hr1G111620) homologo us to the boundary gene LIGULELESS 1 in maize ( LG1 ; ZmSPL4 ), rice OsLG1 ( OsSPL8 ) and hexaploid wheat TaLG1 ( TaSPL8 ) 26 . Similar to the known maize module ( RA2 → WAB1 / BAD1 → LG1 ; 17, 18 , we found that VRS4 / HvRA2 → COM1 → HvLG1 regulat ion appears to be maintained in barley.…”

“…Similar to the known maize module ( RA2 → WAB1 / BAD1 → LG1 ; 17, 18 , we found that VRS4 / HvRA2 → COM1 → HvLG1 regulat ion appears to be maintained in barley. Transcriptome analysis of leaf tissues in a wheat liguleless1 mutant revealed TaSPL8 as a cell wall-related gene 26 . Notably, no spike-branching phenotype was reported for this erected-leaf liguleless mutant, most likely due to genetic redundancy.…”

“…Involvement of COM1 in printing such mechanic a l regulation is supported by our anatomical analysis of palea cell walls and further confirmed by our transcriptome analysis of immature barley spike samples. HvLG1 , HvLSI and genes encoding one LRR-RLK, one CYP450 and two XTHs were among the most downregulated in the mutant and involved in defining cell wall properties 26–28, 31 . The contribution of boundary cell wall mechanics in guiding organogenesis within reproductive tissues has been well described in dicot species 32 .…”