Comparative Transcriptome and Lipidome Reveal That a Low K+ Signal Effectively Alleviates the Effect Induced by Ca2+ Deficiency in Cotton Fibers

Calcium (Ca2+) plays an important role in determining plant growth and development because it maintains cell wall and membrane integrity. Therefore, understanding the role of Ca2+ in carbon and lipid metabolism could provide insights into the dynamic changes in cell membranes and cell walls during the rapid elongation of cotton fibers. In the present study, we found that the lack of Ca2+ promoted fiber elongation and rapid ovule expansion, but it also caused tissue browning in the ovule culture system. RNA-sequencing revealed that Ca2+ deficiency induced cells to be highly oxidized, and the expression of genes related to carbon metabolism and lipid metabolism was activated significantly. All gene members of nine key enzymes involved in glycolysis were up-regulated, and glucose was significantly reduced in Ca2+ deficiency-treated tissues. Ca2+ deficiency adjusted the flowing of glycolysis metabolic. However, low K+ recovered the expression levels of glycolysis genes and glucose content caused by Ca2+ deficiency. Electrospray ionization-tandem mass spectrometry technology was applied to uncover the dynamic profile of lipidome under Ca2+ and K+ interacted conditions. Ca2+ deficiency led to the decrease of fatty acid (FA), diacylglycerol (DAG), glycolipid and the significant increase of triacylglycerol (TAG), phospholipid phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and PC (phosphatidylcholine). Low K+ restored the contents of FA, phospholipids, and glycolipids, effectively relieved the symptoms caused by Ca2+ deficiency, and recovered the development of fiber cells. This study revealed dynamic changes in transcript and metabolic levels and uncovered the signaling interaction of Ca2+ deficiency and low K+ in glycolysis and lipid metabolism during fiber development.