AUTHOR=Collin Anna , Daszkowska-Golec Agata , Kurowska Marzena , Szarejko Iwona 

TITLE=Barley ABI5 (Abscisic Acid INSENSITIVE 5) Is Involved in Abscisic Acid-Dependent Drought Response

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.01138

DOI=10.3389/fpls.2020.01138

ISSN=1664-462X

ABSTRACT=<p>ABA INSENSITIVE 5 (ABI5) is a basic leucine zipper (bZIP) transcription factor which acts in the abscisic acid (ABA) network and is activated in response to abiotic stresses. However, the precise role of barley (<italic>Hordeum vulgare</italic>) ABI5 in ABA signaling and its function under stress remains elusive. Here, we show that <italic>HvABI5</italic> is involved in ABA-dependent regulation of barley response to drought stress. We identified barley TILLING mutants carrying different alleles in the <italic>HvABI5</italic> gene and we studied in detail the physiological and molecular response to drought and ABA for one of them. The <italic>hvabi5.d</italic> mutant, carrying G1751A transition, was insensitive to ABA during seed germination, yet it showed the ability to store more water than its parent cv. “Sebastian” (WT) in response to drought stress. The drought-tolerant phenotype of <italic>hvabi5.d</italic> was associated with better membrane protection, higher flavonoid content, and faster stomatal closure in the mutant under stress compared to the WT. The microarray transcriptome analysis revealed up-regulation of genes associated with cell protection mechanisms in the mutant. Furthermore, HvABI5 target genes: <italic>HVA1</italic> and <italic>HVA22</italic> showed higher activity after drought, which may imply better adaptation of <italic>hvabi5.d</italic> to stress. On the other hand, chlorophyll content in <italic>hvabi5.d</italic> was lower than in WT, which was associated with decreased photosynthesis efficiency observed in the mutant after drought treatment. To verify that <italic>HvABI5</italic> acts in the ABA-dependent manner we analyzed expression of selected genes related to ABA pathway in <italic>hvabi5.d</italic> and its WT parent after drought and ABA treatments. The expression of key genes involved in ABA metabolism and signaling differed in the mutant and the WT under stress. Drought-induced increase of expression of <italic>HvNCED1, HvBG8, HvSnRK2.1</italic>, and <italic>HvPP2C4</italic> genes was 2–20 times higher in <italic>hvabi5.d</italic> compared to “Sebastian”. We also observed a faster stomatal closure in <italic>hvabi5.d</italic> and much higher induction of <italic>HvNCED1</italic> and <italic>HvSnRK2.1</italic> genes after ABA treatment. Together, these findings demonstrate that <italic>HvABI5</italic> plays a role in regulation of drought response in barley and suggest that HvABI5 might be engaged in the fine tuning of ABA signaling by a feedback regulation between biosynthetic and signaling events. In addition, they point to different mechanisms of <italic>HvABI5</italic> action in regulating drought response and seed germination in barley.</p>