中山大学叶绿体氧还系统功能研究新成果

　　

近日，中山大学生命科学学院王金发、王宏斌课题组在叶绿体氧还调控系统的生理功能研究中取得新进展，两项研究成果分别于植物学领域权威期刊The Plant Journal以及Plant Physiology在线发表，博士生刘隽与王鹏均为共同第一作者，王宏斌教授为通讯作者。

叶绿体是植物细胞进行光合作用的场所，其正常发育是植物进行光合作用的前提。光合作用涉及一系列的氧化还原反应，其中位于光合电子传递链末端的Fd（铁氧还蛋白）、FTR（铁氧还蛋白-硫氧还蛋白还原酶）和TRX（硫氧还蛋白）共同组成了光合自养型生物所特有的Fd-FTR-TRX氧还系统，该系统能够将光合作用光反应产生的电信号转化成生物化学能，为固定二氧化碳提供动力。然而，Fd-FTR-TRX氧还系统在植物生长发育中的具体调控功能仍不清楚。

该课题组通过对Fd-FTR-TRX氧还系统的研究发现，Fd2（铁氧还蛋白2）和TRX m（m类硫氧还蛋白）分别在植物适应强光胁迫以及在PSII（光合系统II）复合物生物发生中发挥重要作用。对拟南芥Fd2缺失突变体的研究表明，在长期强光胁迫下，植物通过下调Fd2的表达水平，来促进叶绿体内的多种光保护机制（包括质体氧还信号和环式电子传递等），从而实现植物对逆境的适应。该研究成果于10月7日在线发表于The Plant Journal（DOI:10.1111/tpj.12341）。

同时，通过病毒诱导的基因沉默技术（VIGS技术）对拟南芥TRX m基因家族的研究发现，该家族成员TRX m1，TRX m2和TRX m4通过氧还调控PSII复合物蛋白亚基的寡聚化，共同参与调节PSII复合物的生物发生与叶绿体发育。该研究成果于10月22日在线发表于Plant Physiology（DOI:10.1104/pp.113.228353）。

上述研究不仅有助于更好地理解光合电子传递所介导的氧还调控在叶绿体发育中的调控功能，而且为探索提高农作物光合作用效率的实际应用提供了新思路。相关工作得到了国家自然科学基金与广东省自然科学基金等资助。

这是该课题组在植物逆境生物学方面取得的又一重要进展。2012年，该课题组发现了水稻识别真菌与细菌的双重天然免疫受体，相关研究成果于2012年8月发表于植物学领域权威期刊The Plant Cell，并在2013年9月最新公布的ESI数据库中，被选为全球ESI热点论文（ESI hot papers in the last 2 years）。

原文摘要：

Evidence for a role of chloroplastic m-type thioredoxins in the biogenesis of Photosystem II in Arabidospsis thaliana

Chloroplastic m-type thioredoxins (TRX m) are essential redox regulators in the light regulation of photosynthetic metabolism. However, recent genetic studies have revealed novel functions for TRX m in meristem development, chloroplast morphology, cyclic electron flow, and tetrapyrrole synthesis. The focus of this study is on the putative role of Arabidopsis TRX m1, TRX m2, and TRX m4 in the biogenesis of photosynthetic apparatus. To that end, we investigated the impact of single, double, and triple TRX m deficiency on chloroplast development and the accumulation of thylakoid protein complexes. Intriguingly, only inactivation of three TRX m genes led to pale-green leaves and specifically reduced stability of PSII complex, implying functional redundancy between three TRX m isoforms. In addition, plants silenced for three TRX m genes displayed elevated levels of reactive oxygen species, which in turn interrupted the transcription of photosynthesis-related nuclear genes, but not the expression of chloroplast-encoded PSII core proteins. To dissect the function of TRX m in PSII biogenesis, we showed that TRX m1, TRX m2, and TRX m4 interact physically with minor PSII assembly intermediates as well as with PSII core subunits D1, D2, and CP47. Furthermore, silencing three TRX m genes disrupted the redox status of intermolecular disulfide bonds in PSII core proteins, most notably resulting in elevated accumulation of oxidized CP47 oligomers. Taken together, our results suggest an important role for TRX m1, TRX m2, and TRX m4 proteins in the biogenesis of PSII, and they appear to assist the assembly of CP47 into PSII.

Lysin Motif–Containing Proteins LYP4 and LYP6 Play Dual Roles in Peptidoglycan and Chitin Perception in Rice Innate Immunity

Plant innate immunity relies on successful detection of microbe-associated molecular patterns (MAMPs) of invading microbes via pattern recognition receptors (PRRs) at the plant cell surface. Here, we report two homologous rice (Oryza sativa) lysin motif–containing proteins, LYP4 and LYP6, as dual functional PRRs sensing bacterial peptidoglycan (PGN) and fungal chitin. Live cell imaging and microsomal fractionation consistently revealed the plasma membrane localization of these proteins in rice cells. Transcription of these two genes could be induced rapidly upon exposure to bacterial pathogens or diverse MAMPs. Both proteins selectively bound PGN and chitin but not lipopolysaccharide (LPS) in vitro. Accordingly, silencing of either LYP specifically impaired PGN- or chitin- but not LPS-induced defense responses in rice, including reactive oxygen species generation, defense gene activation, and callose deposition, leading to compromised resistance against bacterial pathogen Xanthomonas oryzae and fungal pathogen Magnaporthe oryzae. Interestingly, pretreatment with excess PGN dramatically attenuated the alkalinization response of rice cells to chitin but not to flagellin; vice versa, pretreatment with chitin attenuated the response to PGN, suggesting that PGN and chitin engage overlapping perception components in rice. Collectively, our data support the notion that LYP4 and LYP6 are promiscuous PRRs for PGN and chitin in rice innate immunity.