Department of Biology, Stanford University, Stanford, California 94305, USA.
Donald Danforth Plant Science Center, St Louis, Missouri 63132, USA.
Plant Cell. 2022 Mar 29;34(4):1207-1225. doi: 10.1093/plcell/koac007.
The spatiotemporal development of somatic tissues of the anther lobe is necessary for successful fertile pollen production. This process is mediated by many transcription factors acting through complex, multi-layered networks. Here, our analysis of functional knockout mutants of interacting basic helix-loop-helix genes Ms23, Ms32, basic helix-loop-helix 122 (bHLH122), and bHLH51 in maize (Zea mays) established that male fertility requires all four genes, expressed sequentially in the tapetum (TP). Not only do they regulate each other, but also they encode proteins that form heterodimers that act collaboratively to guide many cellular processes at specific developmental stages. MS23 is confirmed to be the master factor, as the ms23 mutant showed the earliest developmental defect, cytologically visible in the TP, with the most drastic alterations in premeiotic gene expression observed in ms23 anthers. Notably, the male-sterile ms23, ms32, and bhlh122-1 mutants lack 24-nt phased secondary small interfering RNAs (phasiRNAs) and the precursor transcripts from the corresponding 24-PHAS loci, while the bhlh51-1 mutant has wild-type levels of both precursors and small RNA products. Multiple lines of evidence suggest that 24-nt phasiRNA biogenesis primarily occurs downstream of MS23 and MS32, both of which directly activate Dcl5 and are required for most 24-PHAS transcription, with bHLH122 playing a distinct role in 24-PHAS transcription.
花药体组织的时空发育对于成功产生有活力的花粉是必要的。这个过程由许多转录因子通过复杂的多层次网络介导。在这里，我们分析了玉米（Zea mays）中相互作用的基本螺旋-环-螺旋基因 Ms23、Ms32、基本螺旋-环-螺旋 122（bHLH122）和 bHLH51 的功能敲除突变体，发现雄性育性需要这四个基因，它们在绒毡层（TP）中顺序表达。它们不仅相互调节，而且编码形成异二聚体的蛋白质，这些蛋白质协同作用指导特定发育阶段的许多细胞过程。MS23 被确认为主调控因子，因为 ms23 突变体表现出最早的发育缺陷，在绒毡层中细胞学上可见，在 ms23 花药中观察到的减数分裂前基因表达的变化最为剧烈。值得注意的是，雄性不育的 ms23、ms32 和 bhlh122-1 突变体缺乏 24-nt 相分的二级小干扰 RNA（phasiRNAs）和相应的 24-PHAS 基因座的前体转录本，而 bhlh51-1 突变体具有两种前体和小 RNA 产物的野生型水平。多项证据表明，24-nt phasiRNA 的生物发生主要发生在 MS23 和 MS32 的下游，它们都直接激活 Dcl5，并且是大多数 24-PHAS 转录所必需的，而 bHLH122 在 24-PHAS 转录中发挥独特的作用。
