Sorghum tiller bud growth is repressed by contact with the overlying leaf

Abstract

Basal branching in grasses, or tillering, is an important trait determining both form and function of crops. Although similarities exist between eudicot and grass branching programs, one notable difference is that the tiller buds of grasses are covered by the subtending leaf, whereas eudicot buds are typically unconstrained. The current study shows that contact with the leaf sheath represses sorghum bud growth by providing a mechanical signal that cues the bud to refrain from rapid growth. Leaf removal resulted in massive reprogramming of the bud transcriptome that included signatures of epigenetic modifications and also implicated several hormones in the response. Bud abscisic acid transiently increased, then decreased following leaf removal relative to controls, and abscisic acid was necessary to repress bud growth in the presence of the leaf. Jasmonic acid (JA) levels and signalling increased in buds following leaf removal. Remarkably, application of JA to buds in situ promoted growth. The repression of bud growth by leaf contact shares characteristics of thigmomorphogenic responses in other systems, including the involvement of JA, though the JA effect is opposite. The repression of bud growth by leaf contact may represent a mechanism to time tillering to an appropriate developmental stage of the plant.

The regulatory landscape of a core maize domestication module controlling bud dormancy and growth repression

“…This suggests a function for JAs in suppressing growth in axillary positions, and is consistent with the known effects of JA on suppression of mitosis 48 . These observations, however, contrast with a recent report in sorghum, where JA correlates with tiller bud growth rather than dormancy 33 , underscoring the need for more work on the role of JA in bud dormancy. Interestingly, another known target of TB1, tru1 , also functions to suppress axillary branch elongation, as well as sex determination of the inflorescence, although it is not yet known whether this occurs through a JA-related mechanism.…”

“…Unlike ABA, JA was not implicated in promoting axillary bud dormancy until only recently 31,32 Surprisingly, a recent report indicated that JA may promote bud growth 33 . However, our transcript profiling showed strong evidence that both JA biosynthesis and downstream signaling are affected by tb1/gt1- mediated bud dormancy (Fig.…”

Mechanically induced localization of SECONDARY WALL INTERACTING bZIP is associated with thigmomorphogenic and secondary cell wall gene expression

“…Touch elicits major global changes in gene expression, with 2.5% to 10% of the genes assayed in A. thaliana and poplar differentially expressed (Lee et al, 2005; Pomiès et al, 2017; Van Moerkercke et al, 2019). In sorghum ( Sorghum bicolor ), leaf sheath imposes mechanical constraints on emerging buds, and removing this dramatically altered gene expression, with 42% of genes differentially expressed over a 9 h period (Liu and Finlayson, 2019). Our observations of short term (<2 h) touch responses within stress related pathways align with observations from poplar and A. thaliana , with rapid induction of TCH , biotic, and abiotic stress related genes (Pomiès et al, 2017).…”

Characterization of full-length transcriptome in Saccharum officinarum and molecular insights into tiller development

“…The strong upregulation of LOX genes in this study indicates a mechanism towards high synthesis of key oxylipins involved in tiller growth and development in sugarcane. Jasmonic acid (JA) is a type of oxylipins and several studies have demonstrated that JA contents affect tillering in grass [ 58 , 59 ]. Future studies should investigate developing sugarcane tiller bud samples to clarify whether JA or other types of oxylipins promote tiller development.…”