Heterochromatin de-condensation in companion gametic cells is conserved in both plants and animals. In plants, microspore undergoes asymmetric pollen mitosis (PMI) to produce a vegetative cell (VC) and a generative cell (GC). Subsequently, the GC undergoes pollen mitosis (PMII) to produce two sperm cells (SC). Consistent with heterochromatin de-condensation in the VC, H3K9me2, a heterochromatin mark, is barely detected in VC. However, how H3K9me2 is differentially regulated during pollen mitosis remains unclear. Here, we show that H3K9me2 is gradually evicted from the VC since PMI but remain unchanged in the GC and SC. ARID1, a pollen-specific transcription factor that facilitates PMII, promotes H3K9me2 maintenance in the GC/SC but slows down its eviction in the VC. The genomic targets of ARID1 mostly overlaps with H3K9me2 loci, and ARID1 recruits H3K9 methyltransferase SUVH6. Our results uncover that differential pattern of H3K9me2 between two cell types is regulated by ARID1 during pollen mitosis.

伴配子细胞中的异染色质去浓缩在植物和动物中都是保守的。在植物中，小孢子经历不对称花粉有丝分裂 (PMI)，产生营养细胞 (VC) 和生殖细胞 (GC)。随后，GC 进行花粉有丝分裂 (PMII)，产生两个精子细胞 (SC)。与 VC 中异染色质去浓缩一致，异染色质标记 H3K9me2 在 VC 中几乎检测不到。然而，H3K9me2 在花粉有丝分裂过程中如何受到差异性调节仍不清楚。在这里，我们表明自 PMI 以来 H3K9me2 逐渐从 VC 中逐出，但在 GC 和 SC 中保持不变。 ARID1 是一种花粉特异性转录因子，可促进 PMII，促进 GC/SC 中 H3K9me2 的维持，但减慢其在 VC 中的驱逐。 ARID1 的基因组靶标大部分与 H3K9me2 基因座重叠，并且 ARID1 招募 H3K9 甲基转移酶 SUVH6。我们的结果揭示了两种细胞类型之间 H3K9me2 的差异模式在花粉有丝分裂过程中受到 ARID1 的调节。