Leaf Removal Rapidly Promotes Sorghum Tiller Bud Growth and Alters Bud Hormones and Transcriptome

Tiller buds of grasses like sorghum form in close contact with the overlying leaf. A prior study showed that tiller bud growth was repressed by mechanical signals generated by contact with the leaf, and that removing the leaf permitted robust bud growth. The current study was conducted to better define the rapid changes in bud growth following leaf removal, and to identify potential hormones and pathways associated with the phenomenon. Time course image analyses showed that bud growth was promoted within 6 h of leaf removal. This rapid growth response was associated with increased JA within 2.5 min and with massive reprogramming of the bud transcriptome within 10 min. A role for ERF transcription factors was supported by overrepresentation of differentially expressed ERF genes in the bud transcriptome data, and by the discovery of an ERF promoter motif in highly induced genes. This study provides insights into both the pathways associated with mechanical signaling, and with pathways involved in coordinating the very rapid hormonal and transcriptional changes underlying tiller bud growth. These findings may suggest targets to improve crop resiliency to mechanical stresses (ie- lodging) and to manipulate tiller development for enhanced productivity or end-use.