The development of pollen is a prerequisite for double fertilization in angiosperms. Coat protein complex II (COPII) mediates anterograde transport of vesicles from the endoplasmic reticulum to the Golgi. Components of the COPII complex have been reported to regulate either sporophytic or gametophytic control of pollen development. The Arabidopsis (Arabidopsis thaliana) genome encodes five Sar1 isoforms, the small GTPases essential for COPII formation. By using a dominant negative approach, Sar1 isoforms were proposed to have distinct cargo specificity despite their sequence similarity. Here, we examined the functions of three Sar1 isoforms through analysis of transfer DNA insertion mutants and CRISPR/Cas9-generated mutants. We report that functional loss of Sar1b caused malfunction of tapetum, leading to male sterility. Ectopic expression of Sar1c could compensate for Sar1b loss of function in sporophytic control of pollen development, suggesting that they are interchangeable. Functional distinction between Sar1b and Sar1c may have resulted from their different gene transcription levels based on expression analyses. On the other hand, Sar1b and Sar1c redundantly mediate male gametophytic development such that the sar1b;sar1c microspores aborted at anther developmental stage 10. This study uncovers the role of Sar1 isoforms in both sporophytic and gametophytic control of pollen development. It also suggests that distinct functions of Sar1 isoforms may be caused by their distinct transcription programs.

花粉的发育是被子植物双重受精的先决条件。外壳蛋白复合物II（COPII）介导囊泡从内质网到高尔基体的顺行转运。据报道，COPII复合物的成分可调节花粉发育的孢子控制或配子控制。拟南芥（Arabidopsis thaliana）基因组编码5个Sar1亚型，这是COPII形成所必需的小GTPases。通过使用显性负性方法，Sar1亚型被提议具有独特的货物特异性，尽管它们的序列相似。在这里，我们通过分析转移DNA插入突变体和CRISPR / Cas9产生的突变体检查了三种Sar1亚型的功能。我们报告说Sar1b的功能丧失导致绒毡层失灵，导致雄性不育。Sar1c的异位表达可以补偿Sar1b在花粉发育的孢子控制中的功能丧失，表明它们是可互换的。Sar1b和Sar1c之间的功能差异可能是由于基于表达分析的不同基因转录水平引起的。另一方面，Sar1b和Sar1c冗余地介导了雄配子体发育，因此sar1b ; sar1c小孢子在花药发育阶段10终止。这项研究揭示了Sar1亚型在花粉发育的孢子和配子体控制中的作用。这也表明，Sar1亚型的不同功能可能是由其不同的转录程序引起的。