Evolution and Functional Divergence of SUN Genes in Plants

Area of Science:

• Molecular Biology
• Evolutionary Biology
• Plant Science

Background:

• SUN-domain proteins are essential nuclear membrane proteins involved in critical cellular processes like meiosis and nuclear morphology.
• The evolutionary trajectories and functional diversification of SUN proteins across different taxa remain largely uncharacterized.

Purpose of the Study:

• To investigate the evolutionary history and functional divergence of SUN proteins, particularly within the plant kingdom.
• To characterize the distinct subfamilies of SUN proteins in plants and their specific roles in development.

Main Methods:

• Phylogenetic analysis of 216 SUN proteins from protists, fungi, and plants to identify evolutionary clades.
• Comparative analysis of conserved residues, TM motifs, and exon-intron structures between SUN protein clades.
• Gene expression analysis in cotton and functional studies using virus-induced gene silencing and CRISPR/Cas9 knockout of *GbSUN5*.

Main Results:

• SUN proteins were classified into two monophyletic clades: Cter-SUN and Mid-SUN.
• Mid-SUN proteins diverged into SUN3 and SUN5 subgroups prior to angiosperm evolution; Cter-SUNs retained the SUN1 subfamily.
• Distinct structural features and differential gene duplication/loss rates were observed between clades. SUN5 is specifically expressed in pollen and its disruption leads to increased seed abortion.

Conclusions:

• Significant functional divergence exists between SUN3 and SUN5 proteins.
• SUN5 plays a critical role in plant reproductive development, particularly in seed formation, despite normal pollen viability.