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Journal of Integrative Agriculture  2025, Vol. 24 Issue (9): 3322-3333    DOI: 10.1016/j.jia.2023.12.024
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A naturally occurring 31 bp deletion in TEOSINTE BRANCHED1 causes branched ears in maize

Ling Ai1, 2*, Ju Qiu1, 3*, Jiuguang Wang1*, Mengya Qian1, 4, Tingting Liu1, Wan Cao1, Fangyu Xing1, Hameed Gul1, Yingyi Zhang1, Xiangling Gong1, Jing Li1, Hong Duan1, Qianlin Xiao1#, Zhizhai Liu1, 5#

1 College of Agronomy and Biotechnology, Southwest University, Chongqing 400715, China

2 Dazu No.1 Middle School, Chongqing 402368, China

3 Novogene Co. Ltd., Beijing 100015, China

4 Shishou No.1 Senior School, Shishou 434499, China

5 Engineering Research Center of South Upland Agriculture, Ministry of Education, Chongqing 400715, China

 Highlights 
● A novel mutant of branched ear1 (be1) in maize was characterized, and the abnormal primordia at the very base of female inflorescence was observed to serve as the initiation of branched ears in be1.
TB1 with a be1-specific 31-bp deletion was determined as the candidate, and was further verified to complement the phenotypic performance of branched ears in be1 via the TB1-based edited lines.
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摘要  
与雄花序不同,正常发育的玉米雌花序(或称雌穗)不会形成分枝分生组织(BM)。然而,当fea2/3/4ramosa1/2/3等基因发生突变后,对应的突变体却会形成具有分枝的雌穗。在改变雌穗形态结构的同时,这些目标基因还会同步影响突变体雄穗的正常发育。本研究中,我们鉴定了一个自然发生的雌穗分枝突变体branched ear1be1)。be1的雌穗基部会着生多个分枝穗,但其雄穗却发育正常。并且,be1的分枝穗和主雌穗都能正常授粉结实,形成排列规则的籽粒。be1的这些特性,显著不同于玉米中此前报道的束状穗或RAMOSA型的同类突变体。扫描电镜(SEM)鉴定结果显示,在be1雌穗发育早期,其幼穗基部会着生带有3个生长锥的分生组织,类似于雄穗幼穗的BM。基因定位以及序列比对结果表明,TEOSINTE BRANCHED1TB1)基因是调控be1雌穗分枝表型的候选基因BE1。进一步的验证结果显示,BE1编码区下游存在一段突变体特有的31bp缺失,导致BE1在雌穗幼穗中的表达量显著下调,可能是导致be1雌穗出现分枝的主要原因。我们进一步利用CRISPR/Cas9编辑自交系KN5585的TB1编码区下游区域,在纯合编辑株系中,观察到类似于be1的雌穗分枝表型,表明TB1BE1的目标基因,并将其命名为ZmTB1be1。本研究的结果表明,TB1除了调控玉米的植株形态建成外,在玉米雌穗发育中也发挥着潜在的重要作用。后续有关ZmTB1be1的功能解析,可能为玉米重要驯化基因TB1的相关研究提供新的参考和借鉴。


Abstract  

The female inflorescence, or ear, of maize develops no branch meristem (BM), which differs from the male inflorescence, or tassel.  While the mutations of some well documented genes, such as fea2/3/4 and ramosa1/2/3, can cause the branched architecture of ears in maize, such mutations also change the normal phenotypic performance of the tassels.  In the present study, a natural maize mutant with branched ears, named branched ear1 (be1), was characterized.  be1 shows several branched ears at the base of the central ear with unchanged architecture of the tassels.  Besides, both the branched and central ears of be1 possess regularly arranged kerels.  The phenotypic characteristics of be1 differ completely from those reported mutants of fasciated ears or RAMOSA-like ears in maize.  An SEM survey at the very early development stage showed that meristems with three protrusions, similar to the BM in tassels, were present during the development of the branched ears in be1.  Gene mapping and sequence alignment suggested that TEOSINTE BRANCHED1 (TB1) was the candidate gene of BE1.  Further verification showed that a be1-specific 31 bp deletion at the downstream of BE1 led to statistically reduced expression of this gene in the immature ear, which serves as the potential causal reason for the branched ears of be1.  CRISPR/Cas9-based gene editing downstream of TB1 complemented the phenotypic architecture of branched ears, suggesting that TB1 was the target of BE1, and it was named as ZmTB1be1.  The results of the present study implied a novel function of TB1 in female inflorescence development, rather than shaping the plant architecture in maize.  Meanwhile, further functional dissection of ZmTB1be1 might shed new light on TB1, the most famous domestication related gene in maize.

Keywords:  maize (Zea mays L.)       branched ear1 (be1)       TEOSINTE BRANCHED1 (TB1)       female inflorescence       deletion  
Received: 12 September 2023   Online: 27 December 2023   Accepted: 08 November 2023
Fund: 
This work was supported by the Special Key Project for Technological Innovation and Application Development in Chongqing, China (CSTB2022TIAD-KPX0011), the Special Fund for Youth Team of the Southwest Universities, China (SWU-XJPY202306), the Natural Science Foundation of Chongqing, China (cstc2021jcyj-msxmX0583), and the Fundamental Research Funds for the Central Universities of Southwest University, China (S202210635326). 
About author:  #Correspondence Qianlin Xiao, Tel: +86-23-68251410, E-mail: xiaoql1853@swu.edu.cn; Zhizhai Liu, Tel: +86-23-68251410, E-mail: liu003@swu.edu.cn * These authors contributed equally to this study.

Cite this article: 

Ling Ai, Ju Qiu, Jiuguang Wang, Mengya Qian, Tingting Liu, Wan Cao, Fangyu Xing, Hameed Gul, Yingyi Zhang, Xiangling Gong, Jing Li, Hong Duan, Qianlin Xiao, Zhizhai Liu. 2025. A naturally occurring 31 bp deletion in TEOSINTE BRANCHED1 causes branched ears in maize. Journal of Integrative Agriculture, 24(9): 3322-3333.

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