How BBX22 and HY5 Genes Control Plant Height and Fruit Color in Citrus

Greg Howard
6th July, 2024

How BBX22 and HY5 Genes Control Plant Height and Fruit Color in Citrus

Image Source: Natural Science News, 2024

Key Findings

  • Researchers at Huazhong Agricultural University discovered how BBX22 and HY5 proteins control plant height and pigment in citrus
  • Mutations in BBX22 lead to longer internodes and less pigment, while overexpressing BBX22 results in shorter internodes
  • Applying the growth hormone GA3 can reverse the dwarf effect caused by BBX22 overexpression, confirming BBX22's role in growth regulation
Understanding how plants control their growth and development is crucial for agriculture, especially for crops like citrus that are economically significant. A recent study by researchers at Huazhong Agricultural University has shed light on the molecular mechanisms regulating plant height and internode elongation in citrus species[1]. This study identifies a transcriptional cascade involving B-BOX DOMAIN PROTEIN 22 (BBX22) and ELONGATED HYPOCOTYL 5 (HY5) that finely tunes these traits in citrus. The research highlights that mutations in BBX22 lead to increased internode length and decreased pigment accumulation in Citrus hindsii "SJG". Conversely, overexpressing BBX22 in various citrus species and even in tomato resulted in shorter internodes. This suggests that BBX22 plays a significant role in controlling plant height. Moreover, the application of gibberellin A3 (GA3), a plant hormone known to promote growth, reversed the dwarf phenotype caused by BBX22 overexpression, further confirming BBX22's role in growth regulation. Previous studies have shown that HY5 is a critical regulator of light signaling in plants, influencing various aspects of development[2]. HY5's role was primarily studied in Arabidopsis, where it interacts with COP1, a repressor of photomorphogenic development[2]. However, the new study extends the understanding of HY5 by demonstrating its interaction with BBX22 in citrus. It was found that BBX22 not only activates HY5 but also works as a cofactor, enhancing HY5's ability to regulate target gene expression. This interaction between BBX22 and HY5 is particularly interesting because it shows how these proteins work together to control both internode elongation and pigment accumulation. BBX22 directly binds to and activates the expression of several genes, including HY5, GA2 OXIDASE 8 (GA2ox8), PHYTOENE SYNTHASE 1 (PSY1), and Ruby1. These genes are involved in gibberellin metabolism, carotenoid biosynthesis, and anthocyanin regulation, respectively. The dual role of BBX22 in regulating growth and pigmentation adds a layer of complexity to how plants integrate environmental signals to optimize their development. The findings from Huazhong Agricultural University build on earlier research that identified the importance of HY5 in light signaling and development. For instance, it was previously shown that HY5 requires B-box proteins like BBX20, BBX21, and BBX22 to regulate gene expression effectively[3]. The new study confirms this by showing that BBX22 enhances HY5's function in citrus, thereby controlling both plant height and pigment production. This research not only advances our understanding of plant biology but also has practical implications for agriculture. By manipulating the BBX22-HY5 pathway, it may be possible to breed citrus varieties with desired traits, such as reduced plant height for easier harvesting and enhanced pigment accumulation for better nutritional quality. This could lead to the development of new citrus types that are both dwarf and fortified with health-beneficial compounds, addressing both yield and quality in one go. In summary, the study from Huazhong Agricultural University reveals a critical transcriptional cascade involving BBX22 and HY5 that regulates internode elongation and pigment accumulation in citrus. This builds on previous findings about HY5's role in light signaling and opens new avenues for agricultural innovation through targeted breeding programs.

FruitsGeneticsPlant Science


Main Study

1) A transcriptional cascade involving BBX22 and HY5 finely regulates both plant height and fruit pigmentation in citrus.

Published 3rd July, 2024

Related Studies

2) Molecular interaction between COP1 and HY5 defines a regulatory switch for light control of Arabidopsis development.

Journal: Molecular cell, Issue: Vol 1, Issue 2, Jan 1998

3) Identification of BBX proteins as rate-limiting cofactors of HY5.

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