TheHoja loca1Mutant and AUX/IAA Function in Phytomer Development

Abstract

Auxin plays a vital role in plant organ development, influencing organ initiation and patterning across all axes. The diversity in auxin patterning results from changes in the activities and expression of auxin signaling components, including the AUX/IAA repressors. Higher land plants have multigene AUX/IAA families, which leads to functional redundancy and a lack of phenotype in loss of function mutants. Instead, dominant mutations, which prevent AUX/IAA degradation in response to auxin, have highlighted the importance of these proteins in organ development. Here we report a new dominant AUX/IAA mutant in maize, Hoja loca1 (Oja). Oja has a mutation in the degron motif of ZmIAA28 and affects aerial organ initiation and medio-lateral patterning in the leaf. These phenotypes contrast with other maize AUX/IAA mutants that affect the root or inflorescence only. Oja illustrates the role of auxin signaling in the tight coordination of phytomer unit development and provides evidence of species-specific sub-functionalization of the AUX/IAAs.One Line SummaryThe maize AUX/IAA ZmIAA38 is involved in phytomer coordination, aerial organ initiation and mediolateral patterning, and illustrates species specific sub-functionalization of the AUX/IAAs.

Multiplexed in situ hybridization reveals distinct lineage identities for major and minor vein initiation during maize leaf development

“…This observation could reflect the fact that our dataset does not include genes which are specific for either midvein or lateral vein identity. Alternatively, it suggests that the midvein and lateral veins are not intrinsically different, a suggestion supported by the phenotype of midribless mutants ( 47 , 48 ). By contrast, minor veins are transcriptionally distinct from major veins once procambium is specified, as evidenced by transcript localization profiles (see example of single cells in Fig.…”

Multiplexedin situhybridization reveals distinct lineage identities for major and minor vein initiation during maize leaf development

“…This observation could reflect the fact that our dataset does not include genes which are specific for either midvein or lateral vein identity. Alternatively, it suggests that the midvein and lateral veins are not intrinsically different, a suggestion supported by the phenotype of midribless mutants (45,46). By contrast, minor veins are transcriptionally distinct from major veins once procambium is specified, as evidenced by transcript localisation profiles and the phenotype of loss of function TML1 mutants (25).…”

Developmental regulation of leaf venation patterns: monocot versus eudicots and the role of auxin

“…A clear distinction between midvein development in monocots and eudicots has been revealed by the identification of midribless mutants in monocot species (Rao et al, 1988;Fladung, 1994;Yamaguchi et al, 2004;Strable et al, 2017;Richardson et al, www.newphytologist.com 2020), but not in eudicot species. In wild-type monocot leaves, the midvein is a composite structure comprised of some small veins either side of the median vein and achlorophyllous parenchyma cells (Fig.…”

“…In all of the mutants, the midribless phenotype is caused by a failure to develop the composite midvein at P2, as opposed to a failure to specify the median vein. Causative mutations are found in the DROOPING LEAF genes of maize and rice that encode members of the YABBY family (Yamaguchi et al ., 2004; Strable et al ., 2017) and in an AUX/IAA family member ( ZmIAA28 ) in maize (Richardson et al ., 2020). YABBY genes promote organ growth and expansion (Eshed et al ., 2004) in both monocots and eudicots, particularly during carpel development (Bowman & Smyth, 1999; Yamaguchi et al ., 2004; Strable et al ., 2017), but the recruitment of DROOPING LEAF for localised development and proliferation along the midline of the leaf primordium is monocot‐specific.…”