• Male sterility is an important tool for plant breeding and hybrid seed production. Male‐sterile mutants are largely due to an abnormal development of either the sporophytic or gametophytic anther tissues. Tapetum, a key sporophytic tissue, provides nutrients for pollen development, and its delayed degeneration induces pollen abortion. Numerous bHLH proteins have been documented to participate in the degeneration of the tapetum in angiosperms, but relatively little attention has been given to the evolution of the involved developmental pathways across the phylogeny of land plants.
• A combination of cellular, molecular, biochemical and evolutionary analyses was used to investigate the male fertility control in Medicago truncatula.
• We characterized the male‐sterile mutant empty anther1 (ean1) and identified EAN1 as a tapetum‐specific bHLH transcription factor necessary for tapetum degeneration. Our study uncovered an evolutionarily conserved recruitment of bHLH subfamily II and III(a + c)1 in the regulation of tapetum degeneration. EAN1 belongs to the subfamily II and specifically forms heterodimers with the subfamily III(a + c)1 members, which suggests a heterodimerization mechanism conserved in angiosperms.
• Our work suggested that the pathway of two tapetal‐bHLH subfamilies is conserved in all land plants, and likely was established before the divergence of the spore‐producing land plants.

中文翻译：

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一项关于Medi藜苜蓿雄性育性控制的研究发现，在植物有性生殖中，两个绒毛bHLH亚科在进化上保守地招募。

• 雄性不育是植物育种和杂交种子生产的重要工具。雄性不育突变体主要是由于孢子或配子体花药组织的异常发育。绒毡层是一种主要的孢子体组织，为花粉的发育提供营养，其延迟的变性导致花粉流产。已有文献报道许多bHLH蛋白参与被子植物绒毡层的退化，但是对涉及陆地植物系统发育的相关发育途径的进化的关注却相对较少。
• 细胞，分子，生化和进化分析相结合，用于研究Medi藜苜蓿的雄性育性控制。
• 我们对雄性不育突变体空花药1（ean1）进行了表征，并将EAN1鉴定为绒毡层变性所需的绒毡层特异性bHLH转录因子。我们的研究发现在绒毡层变性的调节中，bHLH家族II和III（a + c）1的进化保守募集。EAN1属于亚家族II，并且与亚家族III（a + c）1成员特别形成异二聚体，这表明被子植物中保守的异二聚化机制。
• 我们的工作表明，两个绒毛－bHLH亚科的途径在所有陆生植物中都得到保留，并且可能是在产芽孢的陆生植物发散之前建立的。