ZmSPAs Modulate Photomorphogenesis and Promote Plant Height in Arabidopsis thaliana

SPAs (suppressors of phyA-105) are key modulators of photomorphogenesis that regulate diverse aspects of plant growth. While the role of SPA proteins in <i>Arabidopsis</i> photomorphogenesis is well-characterized, the functions of their maize (<i>Zea mays</i> L.) homologs (<i>ZmSPAs</i>) remain largely unexplored. Here, we show that <i>ZmSPAs</i> have the typical conserved domains of the SPA family and respond to different light qualities and photoperiodic treatments. Further analysis of the subcellular localization of <i>ZmSPAs</i> showed that <i>ZmSPA1</i> and <i>ZmSPA2</i> were localized to the nucleus, while <i>ZmSPA3</i> and <i>ZmSPA4</i> were localized to both the nucleus and the plasma membrane. The results of tissue-specific expression showed that <i>ZmSPA1</i> and <i>ZmSPA2</i> had the highest relative expression level in silks, while <i>ZmSPA3</i> and <i>ZmSPA4</i> were mainly expressed in leaves. Interestingly, overexpression of <i>ZmSPAs</i> in <i>Arabidopsis</i> promoted hypocotyl elongation in seedlings, inhibited cotyledon expansion in seedlings, and increased plant height in mature plants. The Y2H and LCI results indicate that <i>ZmSPAs</i> have physical interactions with ZmCOP1a, ZmCOP1b, and AtCOP1. These findings reveal the roles of <i>ZmSPAs</i> in regulating photomorphogenesis in <i>Arabidopsis</i> seedlings and plant height development in mature plants, laying a foundation for future investigations into their endogenous functions in maize.