AUTHOR=Zhou Yu Ping , Wu Jing Hui , Xiao Wen Hui , Chen Wei , Chen Qiong Hua , Fan Tian , Xie Chu Ping , Tian Chang-En 

TITLE=Arabidopsis IQM4, a Novel Calmodulin-Binding Protein, Is Involved With Seed Dormancy and Germination in Arabidopsis

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00721

DOI=10.3389/fpls.2018.00721

ISSN=1664-462X

ABSTRACT=<p>Seed dormancy and germination are regulated by complex mechanisms controlled by diverse hormones and environmental cues. Abscisic acid (ABA) promotes seed dormancy and inhibits seed germination and post-germination growth. Calmodulin (CaM) signals are involved with the inhibition of ABA during seed germination and seedling growth. In this study, we showed that <italic>Arabidopsis thaliana</italic> IQM4 could bind with calmodulin 5 (CaM5) both <italic>in vitro</italic> and <italic>in vivo</italic>, and that the interaction was the Ca<sup>2+</sup>-independent type. The IQM4 protein was localized in the chloroplast and the <italic>IQM4</italic> gene was expressed in most tissues, especially the embryo and germinated seedlings. The T-DNA insertion mutants of <italic>IQM4</italic> exhibited the reduced primary seed dormancy and lower ABA levels compared with wild type seeds. Moreover, <italic>IQM4</italic> plays key roles in modulating the responses to ABA, salt, and osmotic stress during seed germination and post-germination growth. T-DNA insertion mutants exhibited ABA-insensitive and salt-hypersensitive phenotypes during seed germination and post-germination growth, whereas <italic>IQM4</italic>-overexpressing lines had ABA- and osmotic-hypersensitive, and salt-insensitive phenotypes. Gene expression analyses showed that mutation of <italic>IQM4</italic> inhibited the expression of ABA biosynthetic genes <italic>NCED6</italic> and <italic>NCED9</italic>, and seed maturation regulators <italic>LEC1, LEC2, ABI3</italic>, and <italic>ABI5</italic> during the silique development, as well as promoted the expression of <italic>WRKY40</italic> and inhibited that of <italic>ABI5</italic> in ABA-regulated seed germination. These observations suggest that IQM4 is a novel Ca<sup>2+</sup>-independent CaM-binding protein, which is positively involved with seed dormancy and germination in <italic>Arabidopsis</italic>.</p>