Brassica Rapa SR45a Regulates Drought Tolerance via the Alternative Splicing of Target Genes

Abstract

The emerging evidence has shown that plant serine/arginine-rich (SR) proteins play a crucial role in abiotic stress responses by regulating the alternative splicing (AS) of key genes. Recently, we have shown that drought stress enhances the expression of <i>SR45a</i> (also known as <i>SR-like 3</i>) in <i>Brassica rapa.</i> Herein, we unraveled the hitherto unknown functions of <i>BrSR45a</i> in drought stress response by comparing the phenotypes, chlorophyll a fluorescence and splicing patterns of the drought-responsive genes of Arabidopsis <i>BrSR45a</i> overexpressors (OEs), homozygous mutants (SALK_052345), and controls (Col-0). Overexpression and loss of function did not result in aberrant phenotypes; however, the overexpression of <i>BrSR45a</i> was positively correlated with drought tolerance and the stress recovery rate in an expression-dependent manner. Moreover, OEs showed a higher drought tolerance index during seed germination (38.16%) than the control lines. Additionally, the overexpression of <i>BrSR45a</i> induced the expression of the drought stress-inducible genes <i>RD29A, NCED3</i>, and <i>DREB2A</i> under normal conditions. To further illustrate the molecular linkages between <i>BrSR45a</i> and drought tolerance, we investigated the AS patterns of key drought-tolerance and <i>BrSR45a</i> interacting genes in OEs, mutants, and controls under both normal and drought conditions. The splicing patterns of <i>DCP5, RD29A, GOLS1, AKR, U2AF,</i> and <i>SDR</i> were different between overexpressors and mutants under normal conditions. Furthermore, drought stress altered the splicing patterns of <i>NCED2, SQE, UPF1</i>, <i>U4/U6-U5 tri-snRNP</i>-<i>associated protein</i>, and <i>UPF1</i> between OEs and mutants, indicating that both overexpression and loss of function differently influenced the splicing patterns of target genes. This study revealed that <i>BrSR45a</i> regulates the drought stress response via the alternative splicing of target genes in a concentration-dependent manner.