Genetic control of branching patterns in grass inflorescences

Abstract

Inflorescence branching in the grasses controls the number of florets and hence the number of seeds. Recent data on the underlying genetics come primarily from rice and maize, although new data are accumulating in other systems as well. This review focuses on a window in developmental time from the production of primary branches by the inflorescence meristem through to the production of glumes, which indicate the transition to producing a spikelet. Several major developmental regulatory modules appear to be conserved among most or all grasses. Placement and development of primary branches is controlled by conserved auxin regulatory genes. Subtending bracts are repressed by a network including TASSELSHEATH4, and axillary branch meristems are regulated largely by signaling centers that are adjacent to but not within the meristems themselves. Gradients of SBP-like and APETALA2-like proteins and their microRNA regulators extend along the inflorescence axis and the branches, governing the transition from production of branches to production of spikelets. The relative speed of this transition determines the extent of secondary and higher order branching. This inflorescence regulatory network is modified within individual species, particularly as regards formation of secondary branches. Differences between species are caused both by modifications of gene expression and regulators and by presence or absence of critical genes. The unified networks described here may provide tools for investigating orphan crops and grasses other than the well-studied maize and rice.

Systematic mining and functional analysis of factors regulating wheat spike development for breeding selection

“…Whereas, MADS box TFs are outstanding at FOP stage of cluster 5 (Figures 3B and 3C). Such expression pattern fits well with the spatiotemporal switch of meristem identities in the context of hormone regulation (Kellogg, 2022;Koppolu et al, 2022), and indicates potential importance of individual TFs family in driving the transcriptional network that governing spike formation.…”

QTL mapping identifies novel major loci for kernel row number-associated ear fasciation, ear prolificacy and tillering in maize (Zea mays L.)

“…For instance, ZmFEA4 encodes a basic leucine zipper domain (bZIP) transcription factor that is expressed in the shoot meristem peripheral zone and is likely involved in cell transiting from SAM to organ primordium ( Kitagawa and Jackson, 2019 ); the SQUAMOSA PROMOTER BINDING (SBP)-box transcription factors unbranched2 ( UB2 ) and unbranched3 ( UB3 ) are expressed in the initiating leaf primordia and the base of the SAM and control lateral organs initiation ( Chuck et al., 2014 ). Finally, ear shape is also under the control of genes expressed later in development, at the inflorescence or even floret meristem levels, including ramosa1 ( ra1 ), ra2 and ra3 ( Vollbrecht et al., 2005 ; Kellogg, 2022 ), or growth regulating factor-interacting factor1 ( gif1 . Zhang et al., 2018 ), which were shown to control inflorescence (tassel and ear) branching and, when mutated, to produce multiple-tip or branched ears.…”

Tracing the Evolution of the SEPALLATA Subfamily across Angiosperms Associated with Neo- and Sub-Functionalization for Reproductive and Agronomically Relevant Traits

“…Most angiosperms produce flowers arranged in diversified clusters termed inflorescences [ 17 , 18 ], which are orchestrated by the inflorescence meristem (IM) and, eventually, by a subsequent hierarchical order of specialized reproductive meristems, such as the branch meristems (BMs) [ 19 , 20 , 21 ]. The relevant products of most crops and ornamental plants are their fruits and seeds or flowers, respectively.…”