The Impact of Fasciation on Maize Inflorescence Architecture

Abstract

How functional genetics research can be applied to improving crop yields is a timely challenge. One of the most direct methods is to produce larger inflorescences with higher productivity, which should be accompanied by a balance between stem cell proliferation and lateral organ initiation in meristems. Unbalanced proliferation of stem cells causes the fasciated inflorescences, which reflect the abnormal proliferation of meristems, derived from the Latin word ‘fascis’, meaning ‘bundle’. Maize, a model system for grain crops, has shown tremendous yield improvements through the mysterious transformation of the female inflorescence during domestication. In this review, we focus on maize inflorescence architecture and highlight the patterns of fasciation, including recent progress.

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

“…We phenotyped ear fasciation using four approaches, namely collecting the rate between the minor and the major cob diameters, ear ovality or flatness, kernel row disorder index and an ear fasciation index. Thus, our phenotyping approaches covered well the different ways ear fasciation manifests, namely cob flatness and kernel disorder as shown previously (Mendes-Moreira et al, 2015;Kim et al, 2022). Confirming other authors' observations, cob ovality/flatness and kernel row disorder correlated, and correlated also with ear fasciation index.…”

“…By comparing QTL supporting intervals from our and other studies with the genomic positions of inflorescence-related genes we shortlisted candidate genes possibly involved in controlling ear fasciation QTLs (Figure 4A, Supplementary Tables 5, 6). The maize historical tassel and ear mutant ra1, encoding a zincfinger transcriptional factor and producing ear and tassel with increased branches (Vollbrecht et al, 2005;Kim et al, 2022) maps only 0.5 Mb away from the QTL cluster region including qFas7, and within the QTL supporting interval of qKRN7.1. 7, 8.…”

“…This feedback mechanism keeps meristem size under control and appears to be largely conserved in maize. For instance, maize CLV3/EMBRYO-SURROUNDING REGION7 ( ZmCLE7 ) is a CLV3 ortholog; THICK TASSEL DWARF1 ( TD1 ) and FASCIATED EAR2 ( FEA2 ) encode receptor-like proteins related with CLV1 and CLV2, and regulates the size of the ear IM and SAM growth; ZmWUS1 seems to be a direct WUS ortholog and is expressed in the late vegetative SAM ( Wu et al., 2018 ; Kitagawa and Jackson, 2019 ; Kim et al., 2022 ). Genes affecting meristem size and involved in ear fasciation and acting outside the CLV3-WUS loop have also been described.…”

“…Similarly, mutations in CLV genes in Brassica resulted in higher number of locules in fruits, leading to higher yield ( Fan et al., 2014 ; Xiao et al., 2018 ). In maize, ear fasciation has been suggested as a potential target for increasing ear size and/or number of kernels per ear under the expectation that a larger SAM should lead to a wider ear meristem eventually harboring more spikelet pair meristems and thus kernel rows ( Otegui and Bonhomme, 1998 ; Somssich et al., 2016 ; Kim et al., 2022 ; Li et al., 2022 ). However, accumulating evidences indicate that strong ear fasciation alleles do not improve productivity because they usually induce a shorter, stunted ear; instead, weaker fasciation alleles show more potential ( Bommert et al., 2013b ; Je et al., 2016 ; Kim et al., 2022 ; Ortez et al., 2022 ).…”

“…In maize, ear fasciation has been suggested as a potential target for increasing ear size and/or number of kernels per ear under the expectation that a larger SAM should lead to a wider ear meristem eventually harboring more spikelet pair meristems and thus kernel rows ( Otegui and Bonhomme, 1998 ; Somssich et al., 2016 ; Kim et al., 2022 ; Li et al., 2022 ). However, accumulating evidences indicate that strong ear fasciation alleles do not improve productivity because they usually induce a shorter, stunted ear; instead, weaker fasciation alleles show more potential ( Bommert et al., 2013b ; Je et al., 2016 ; Kim et al., 2022 ; Ortez et al., 2022 ). In line with this evidence, quantitative genetic variation for ear fasciation was analyzed using QTL mapping ( Mendes-Moreira et al., 2015 ) and, in a different study, a QTL for kernel row number (KRN) was shown to correspond to ZmFEA2 ( Bommert et al., 2013b ).…”