MADS box transcription factors (TFs) are subdivided into type I and II based on phylogenetic analysis. The type II TFs regulate floral organ identity and flowering time, but type I TFs are relatively less characterized. Here, we report the functional characterization of two type I MADS box TFs in rice (Oryza sativa), MADS78 and MADS79 Transcript abundance of both these genes in developing seed peaked at 48 h after fertilization and was suppressed by 96 h after fertilization, corresponding to syncytial and cellularized stages of endosperm development, respectively. Seeds overexpressing MADS78 and MADS 79 exhibited delayed endosperm cellularization, while CRISPR-Cas9-mediated single knockout mutants showed precocious endosperm cellularization. MADS78 and MADS 79 were indispensable for seed development, as a double knockout mutant failed to make viable seeds. Both MADS78 and 79 interacted with MADS89, another type I MADS box, which enhances nuclear localization. The expression analysis of Fie1, a rice FERTILIZATION-INDEPENDENT SEED-POLYCOMB REPRESSOR COMPLEX2 component, in MADS78 and 79 mutants and vice versa established an antithetical relation, suggesting that Fie1 could be involved in negative regulation of MADS78 and MADS 79 Misregulation of MADS78 and MADS 79 perturbed auxin homeostasis and carbon metabolism, as evident by misregulation of genes involved in auxin transport and signaling as well as starch biosynthesis genes causing structural abnormalities in starch granules at maturity. Collectively, we show that MADS78 and MADS 79 are essential regulators of early seed developmental transition and impact both seed size and quality in rice.

中文翻译：

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MADS78和MADS79是水稻早期种子发育的重要调控因子。

根据系统发育分析，MADS盒转录因子（TFs）分为I型和II型。II型TF调节花器官的身份和开花时间，但I型TF的特征相对较少。在这里，我们报道了水稻（Oryza sativa）中两个I型MADS box TFs的功能特性，MADS78和MADS79这两个基因在发育种子中的转录丰度在受精后48 h达到峰值，并在受精后96 h被抑制，相当于胚乳发育的合胞期和细胞化阶段。过度表达MADS78和MADS 79的种子表现出延迟的胚乳细胞化，而CRISPR-Cas9介导的单敲除突变体表现出早熟的胚乳细胞化。MADS78和MADS 79对于种子发育必不可少，因为双敲除突变体未能产生可行的种子。MADS78和79都与另一种I型MADS盒MADS89相互作用，从而增强了核的定位。Fie1，一种水稻受精的种子-多聚体阻遏物复合物2，在MADS78和79个突变体中的表达分析，反之亦然，这表明Fie1可能参与了MADS78和MADS的负调控79 MADS78和MADS的失调79种植物生长素的稳态和碳代谢紊乱，这由生长素运输和信号转导相关基因的失调以及淀粉生物合成基因成熟导致淀粉颗粒结构异常所证明。总体而言，我们表明MADS78和MADS 79是早期种子发育过渡的必需调节剂，并且会影响水稻的种子大小和质量。