Transcription factor OsbZIP49 controls tiller angle and plant architecture through the activation of indole-3-acetic acid-amido synthetases in rice

Authors: DING, CHAOHUI - Fujian Agricultural & Forestry University; LIN, XIANHUI - Fujian Agricultural & Forestry University; ZUO, YING - Fujian Agricultural & Forestry University; YU, ZHILIN - Fujian Agricultural & Forestry University; LU, YIPING - Fujian Agricultural & Forestry University; CHEN, XU - Fujian Agricultural & Forestry University; Baerson, Scott; Pan, Zhiqiang - Peter; ZENG, RENSEN - Fujian Agricultural & Forestry University; SONG, YUANYUAN - Fujian Agricultural & Forestry University

Submitted to: The Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2021
Publication Date: 9/23/2021
Citation: Ding, C., Lin, X., Zuo, Y., Yu, Z., Lu, Y., Chen, X., Baerson, S.R., Pan, Z., Zeng, R., Song, Y. 2021. Transcription factor OsbZIP49 controls tiller angle and plant architecture through the activation of indole-3-acetic acid-amido synthetases in rice. The Plant Journal. https://doi.org/10.1111/tpj.15515.
DOI: https://doi.org/10.1111/tpj.15515

Interpretive Summary: Plant architecture represents an important strategy for plant adaptation to stressful environments. Rice yield is closely associated with its architecture, which is defined by tillering number and angle, internode elongation, panicle morphology, leaf angle and the lengths of leaf blades and sheaths. In this report, an evidence is provided that a transcription factor, OsbZIP49 in rice plants, plays a significant role in the regulation of plant architecture via regulating auxin homeostasis. Over-expression of OsbZIP49 in rice plants resulted in increased tiller angles and reduced shoot gravitropism. In contrast, knockout mutants of OsbZIP49 showed increased free auxin contents, enhanced signaling in shoot bases upon gravistimulation and exhibited a compact growth phenotype. Taken together, these results provide significant insight concerning the role that auxin homeostasis plays in determining tiller angle and overall plant architecture in rice.

Technical Abstract: Tiller angle is an important determinant of plant architecture in rice (Oryza sativa L.). Auxins play a critical role in various aspects of plant architecture, including the regulation of tiller angle, plant height and shoot gravitropism. However, the metabolic and signaling mechanisms underlying the regulation of tiller angle and shoot gravitropism by auxins are still largely unknown. In this study, we have identified a member of the bZIP family of TGA class transcription factors, OsbZIP49, which participates in the regulation of plant architecture and is specifically expressed in gravity-sensing tissues of rice, including the shoot base, at nodes and within the lamina joint. Transgenic rice plants overexpressing OsbZIP49 displayed a spreading-grown phenotype with reduced plant height and internode length. In contrast, CRISPR/Cas9 mediated knockout of OsbZIP49 resulted in a compact architecture. Follow-up studies indicated that the effects of OsbZIP49 on tiller angles are mediated through changes in shoot gravitropic responses. Additionally, we determined that OsbZIP49 activates the expression of indole-3-acetic acid-amido synthetases OsGH3-2 and OsGH3-13 by directly binding to TGACG motifs located within the promoters of both genes. Increased GH3-catalysed IAA conjugation activity in rice transformants overexpressing OsbZIP49 resulted in the accumulation of IAA-Asp and IAA-Glu, and a reduction in local auxin, tryptamine and IAA-Glc levels. Exogenous IAA or NAA partially restored shoot gravitropism responses in OsbZIP49-overexpressing plants. CRISPR/Cas9 mediated knockout of OsbZIP49 led to reduced expression of both OsGH3-2 and OsGH3-13 within the shoot base, and increased accumulation of IAA and increased OsIAA20 expression levels were observed in transformants following gravistimulation. Taken together, the present results reveal the role transcription factor OsbZIP49 plays in determining plant architecture, primarily due to its influence on local auxin homeostasis.