Functional Analysis of Sporophytic Transcripts Repressed by the Female Gametophyte in the Ovule of Arabidopsis thaliana

To investigate the genetic and molecular regulation that the female gametophyte could exert over neighboring sporophytic regions of the ovule, we performed a quantitative comparison of global expression in wild-type and nozzle/sporocyteless (spl) ovules of Arabidopsis thaliana (Arabidopsis), using Massively Parallel Signature Sequencing (MPSS). This comparison resulted in 1517 genes showing at least 3-fold increased expression in ovules lacking a female gametophyte, including those encoding 89 transcription factors, 50 kinases, 25 proteins containing a RNA-recognition motif (RRM), and 20 WD40 repeat proteins. We confirmed that eleven of these genes are either preferentially expressed or exclusive of spl ovules lacking a female gametophyte as compared to wild-type, and showed that six are also upregulated in determinant infertile1 (dif1), a meiotic mutant affected in a REC8-like cohesin that is also devoided of female gametophytes. The sporophytic misexpression of IOREMPTE, a WD40/transducin repeat gene that is preferentially expressed in the L1 layer of spl ovules, caused the arrest of female gametogenesis after differentiation of a functional megaspore. Our results show that in Arabidopsis, the sporophytic-gametophytic cross talk includes a negative regulation of the female gametophyte over specific genes that are detrimental for its growth and development, demonstrating its potential to exert a repressive control over neighboring regions in the ovule.为探究雌配子体对邻近胚珠孢子体区域的遗传与分子调控机制，我们利用大规模平行标签测序（Massively Parallel Signature Sequencing, MPSS）对拟南芥（Arabidopsis thaliana）野生型与nozzle/sporocyteless（spl）突变体胚珠的全局基因表达谱开展了定量比较。本次比较共筛选出1517个在缺失雌配子体的spl突变体胚珠中表达量上调至少3倍的基因，其中包含89个转录因子编码基因、50个激酶编码基因、25个含RNA识别基序（RNA-recognition motif, RRM）的蛋白编码基因，以及20个WD40重复蛋白编码基因。我们验证了其中11个基因在缺失雌配子体的spl突变体胚珠中相较于野生型呈优势表达或特异性表达，并发现6个基因在决定不育1（determinant infertile1, dif1）突变体胚珠中同样上调；dif1是一类受REC8类黏连蛋白影响的减数分裂突变体，同样缺失雌配子体。IOREMPTE作为一种WD40/转导蛋白重复基因，在spl突变体胚珠的L1层呈优势表达；该基因在孢子体中的异常表达会导致功能大孢子分化后雌配子体发生发育停滞。本研究结果表明，在拟南芥中，孢子体-配子体交叉对话包含雌配子体对特定基因的负调控——这些基因的异常表达会对雌配子体的生长发育产生不利影响；这证明雌配子体具备对胚珠内邻近区域施加抑制性调控的潜在能力。