Alternative Splicing of SCL30a Generates Distinct Isoforms to Modulate ABA Signaling in Arabidopsis

Area of Science:

• Plant molecular biology
• Gene regulation
• Post-transcriptional modification

Background:

• Alternative splicing (AS) and nonsense-mediated decay (NMD) are crucial post-transcriptional regulatory mechanisms.
• Serine/arginine-rich (SR) proteins in plants are involved in development and stress responses, especially abscisic acid (ABA) signaling.
• Functional differences among SR protein splice isoforms are not well understood.

Purpose of the Study:

• To investigate the alternatively spliced isoforms of the plant-specific SR protein SCL30a in Arabidopsis thaliana.
• To elucidate the roles of different SCL30a isoforms in ABA signaling pathways.
• To identify downstream targets of SCL30a in ABA responses.

Main Methods:

• Third-generation long-read transcriptome sequencing to identify SCL30a transcripts.
• Nonsense-mediated decay (NMD) stability assays and subcellular localization analyses.
• Functional analyses using loss-of-function mutants, complementation, and overexpression lines, coupled with transcriptome analysis and genetic rescue experiments.

Main Results:

• Five alternatively spliced SCL30a transcripts were identified; two are rapidly degraded via NMD due to premature termination codons (PTCs).
• Three stable isoforms (SCL30a.1, SCL30a.4, SCL30a.5) localize to the nucleus and positively regulate ABA signaling.
• scl30a mutants show reduced ABA sensitivity, while overexpression of stable isoforms enhances it; SnRK2.6 expression is altered and its overexpression rescues mutant phenotypes.

Conclusions:

• SCL30a isoforms exhibit distinct regulatory roles, with stable nuclear-localized forms acting as positive regulators of ABA signaling.
• The study identifies SCL30a as a key player in ABA responses in Arabidopsis thaliana.
• SnRK2.6 is proposed as a candidate downstream effector in SCL30a-mediated ABA signaling.