A Starch Phosphorylase, ZmPHOH, Improves Photosynthetic Recovery from Short-Term Cold Exposure in Maize

The photosynthetic system of maize (<i>Zea mays</i>) leaves is sensitive to low temperatures and suffers from irreversible damage induced by cold exposure, making cold stress a major factor limiting maize yield. Identifying genes that improve the recovery of photosynthesis from low temperatures in maize will help enhance the cold tolerance of this crop and ensure stable yields. Here, we demonstrate the role of <i>starch phosphorylase 2</i> (<i>ZmPHOH</i>) in promoting photosynthetic recovery from cold damage. <i>Chlorotic leaf3</i> (<i>chl3</i>), a null mutant of <i>ZmPHOH</i>, which undergoes chlorophyll degradation and chlorosis earlier than under normal growth conditions after brief exposure to 8 °C and restoration to normal. We determined that <i>chl3</i> plants could not repair the damage to their photosynthetic system caused by short-term cold exposure after the temperature returned to normal. Metabolome and transcriptome profiling indicated that the soluble sugar content in <i>chl3</i> leaves was significantly increased after cold treatment and could not be catabolized promptly, leading to repression of photosynthetic gene expression. Our results reveal that ZmPHOH enhances post-cold photosynthetic recovery by promoting the decomposition and metabolism of soluble sugars, thereby regulating the low-temperature resilience in maize, which provides new insights into the chilling tolerance mechanism of maize.