A plant‐specific HUA 2‐ LIKE ( HULK ) gene family in A rabidopsis thaliana is essential for development

• Published in: The Plant journal : for cell and molecular biology Vol. 80; no. 2; pp. 242 - 254
• Main Authors: Jali, Sathya S., Rosloski, Sarah M., Janakirama, Preetam, Steffen, Joshua G., Zhurov, Vladimir, Berleth, Thomas, Clark, Richard M., Grbic, Vojislava
• Format: Journal Article
• Language: English
• Published: 01.10.2014
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.12629

In A rabidopsis thaliana , the HUA 2 gene is required for proper expression of FLOWERING LOCUS  C ( FLC ) and AGAMOUS , key regulators of flowering time and reproductive development, respectively. Although HUA 2 is broadly expressed, plants lacking HUA 2 function have only moderately reduced plant stature, leaf initiation rate and flowering time. To better understand HUA 2 activity, and to test whether redundancy with similar genes underlies the absence of strong phenotypes in HUA 2 mutant plants, we identified and subsequently characterized three additional HUA 2‐ LIKE ( HULK ) genes in A rabidopsis. These genes form two clades ( HUA 2 / HULK 1 and HULK 2 / HULK 3 ), with members broadly conserved in both vascular and non‐vascular plants, but not present outside the plant kingdom. Plants with progressively reduced HULK activity had increasingly severe developmental defects, and plants homozygous for loss‐of‐function mutations in all four HULK genes were not recovered. Multiple mutants displayed reproductive, embryonic and post‐embryonic abnormalities, and provide detailed insights into the overlapping and unique functions of individual HULK genes. With regard to flowering time, opposing influences were apparent: hua2 hulk1 plants were early‐flowering, while hulk2 hulk3 mutants were late‐flowering, and hua2 acted epistatically to cause early flowering in all combinations. Genome‐wide expression profiling of mutant combinations using RNA ‐ S eq revealed complex transcriptional changes in seedlings, with FLC , a known target of HUA 2 , among the most affected. Our studies, which include characterization of HULK expression patterns and subcellular localization, suggest that the HULK genes encode conserved nuclear factors with partially redundant but essential functions associated with diverse genetic pathways in plants.