THE Arabidopsis TRANSCRIPTION FACTOR ATHB22 IS INVOLVED IN GERMINATION AND PLANT GROWTH

CHAN RL; TRIONFINI V; WELCHEN E; ATTALLAH C

Congreso; LVI Annual Meeting Argentine Society for Biochemistry and Molecular Biology (SAIB); 2020

AtHB22 (Arabidopsis thaliana Homeobox 22) is a transcription factor (TF) belonging to the HD-Zip I (HomeodomainLeucine Zipper I) family of Arabidopsis thaliana. Members of this family have been broadly associated with developmentalprocesses in response to different environmental factors. To understand the role of AtHB22, we obtained and studied byhistochemistry transgenic plants carrying a segment of its promoter (pHB22) fused to the β-glucuronidase (GUS) reportergene. GUS expression driven by the pHB22 promoter was discretely observed in the shoot apical meristem at 4, 8, and 12 daysafter sowing, at the edges of cotyledons, in rosette petioles, cauline leaf margins, axillary buds, sepal margins, and floralpedicels. No GUS expression was detected in root tissues or siliques in pHB22:GUS plants. Moreover, we characterizedinsertional athb22 mutant plants, analyzing the impact of lacking this protein at different stages of Arabidopsis development.The athb22 mutants exhibited significantly shorter roots in comparison to wild-type (WT) seedlings grown on in vitro MSmedium-plates. The athb22 plants also exhibited a marked delay in germination and higher ABA-sensitivity compared to WTplants. Lack of AtHB22 also generates seedlings with longer hypocotyls than WT plants at the same age. No differences weredetected in the leaf area neither in the number of leaves nor in the flower developmental transition time when plants were grown on soil under control conditions. Our results suggest that AtHB22 is a positive regulator of germination and could beinvolved in the plant response to the phytohormone ABA during this developmental stage. Moreover, AtHB22 acts as a positiveregulator of root growth and could be involved in leaf morphogenesis. In this sense, the AtHB22 expression pattern describedhere is similar to that of its paralog AtHB51, which has been previously reported as essential for leaf morphogenesis and bractformation. Interestingly, AtHB51 was associated with the endoreduplication process in stipules. More efforts have to be doneto deepen the role of AtHB22 in the development of Arabidopsis under normal growth conditions or during stressful situations,and its possible interaction with other members of the HD-Zip 1 family during these processes.