Studies on the Rice LEAF INCLINATION1 (LC1), an IAA–amido Synthetase, Reveal the Effects of Auxin in Leaf Inclination Control

Abstract

The angle of rice leaf inclination is an important agronomic trait and closely related to the yields and architecture of crops. Although few mutants with altered leaf angles have been reported, the molecular mechanism remains to be elucidated, especially whether hormones are involved in this process. Through genetic screening, a rice gain-of-function mutant leaf inclination1, lc1-D, was identified from the Shanghai T-DNA Insertion Population (SHIP). Phenotypic analysis confirmed the exaggerated leaf angles of lc1-D due to the stimulated cell elongation at the lamina joint. LC1 is transcribed in various tissues and encodes OsGH3-1, an indole-3-acetic acid (IAA) amido synthetase, whose homolog of Arabidopsis functions in maintaining the auxin homeostasis by conjugating excess IAA to various amino acids. Indeed, recombinant LC1 can catalyze the conjugation of IAA to Ala, Asp, and Asn in vitro, which is consistent with the decreased free IAA amount in lc1-D mutant. lc1-D is insensitive to IAA and hypersensitive to exogenous BR, in agreement with the microarray analysis that reveals the altered transcriptions of genes involved in auxin signaling and BR biosynthesis. These results indicate the crucial roles of auxin homeostasis in the leaf inclination control.

Dynamic Cytology and Transcriptional Regulation of Rice Lamina Joint Development

“…To further study the mechanism of auxin effects in regulating lamina joint development, a gain-of-function mutant, lc1-D (leaf inclination 1; which encodes OsGH3-1, an IAA amino synthetase), which was identified from the Shanghai T-DNA Insertion Population (Fu et al, 2009) and which presents a reduced auxin level and enlarged leaf angles due to the increased cell elongation in the adaxial surface of the lamina joint (Zhao et al, 2013), was used. Comparison of transcriptomes of the lamina joint of lc1-D and its corresponding original cultivar control, cv ZH11, identified 319 up-regulated and 254 down-regulated genes in lc1-D. Interestingly, 55% of the up-regulated genes (175) and 34% of the down-regulated genes (86) in lc1-D are detected in DEGs along with lamina joint development ( Fig.…”

“…Transgenic rice overexpressing OsARF19 shows enlarged leaf inclination due to the increased expression level of GH3s and the decreased free IAA content (Zhang et al, 2015), and overexpression of OsIAA1 results in the increased leaf angle (Song et al, 2009), suggesting the negative effects of auxin in leaf inclination. Interestingly, most auxin-related mutants present changed BR sensitivity (Song et al, 2009;Zhao et al, 2013;Zhang et al, 2015), and the inclination by treatment with brassinolide alone is suppressed by an inhibitor of IAA transport (Cao and Chen, 1995) or promoted by additional IAA (Han et al, 1997), suggesting a complex regulation of phytohormones in lamina joint development. In addition, BR-induced leaf inclination is accompanied by ethylene production and inhibited by an inhibitor of 1-aminocyclopropane-1-carboxylic acid oxidase (Cao and Chen, 1995) or suppressed by treatment with abscisic acid (ABA) and gibberellin (GA) (Han et al, 1997;Tong et al, 2014), further indicating that phytohormones synergistically and antagonistically regulate lamina joint development and leaf inclination.…”

“…Deficiency of lamina joint structure (Lee et al, 2007), suppressed longitudinal elongation of adaxial parenchyma cells, and increased division of abaxial sclerenchyma cells of the lamina joint (Zhang et al, 2009a;Sun et al, 2015) result in leaf erectness. Conversely, increased expansion or proliferation of adaxial parenchyma cells leads to increased leaf inclination (Zhao et al, 2010(Zhao et al, , 2013Zhang et al, 2015). Abnormal vascular bundle formation and cell wall composition also result in changed leaf angle (Ning et al, 2011).…”

“…Auxin homeostasis and signaling regulate leaf inclination, and gain-of-function mutants or transgenic plants overexpressing GH3 family members, including OsGH3-1, OsGH3-2, OsGH3-5, and OsGH3-13, present reduced auxin levels and enlarged leaf angles (Zhang et al, 2009b(Zhang et al, , 2015Du et al, 2012;Zhao et al, 2013). Overexpression of miR393a/b, which suppresses the expression of OsAFB2 or OsTIR1, leads to the enlarged inclination of flag leaf (Bian et al, 2012).…”

Transcriptomic Analyses Indicate That Maize Ligule Development Recapitulates Gene Expression Patterns That Occur during Lateral Organ Initiation

“…These data are consistent with previous reports that ZmPIN1a-YFP accumulates in the PLB (Moon et al, 2013) (Figures 1I and 1J). Three paralogous GRETCHEN HAGEN3 (GH3)-like genes, which are predicted to encode IAAamide-synthetase proteins that function to convert the auxin IAA into biologically inactive conjugates (Zhao et al, 2013), are also highly upregulated in the ligule and downregulated in lg1-R mutants ( Figure 4D). Intriguingly, misexpression of a rice (Oryza sativa) homolog of GH3 conditions mutant phenotypes at the blade-sheath boundary that alter leaf inclination (Zhao et al, 2013).…”