State Key Laboratory for Crop Genetics and Germplasm Enhancement, Jiangsu Plant Gene Engineering Research Center, Nanjing Agricultural University, Nanjing 210095, China.
State Key Laboratory of Crop Gene Resources and Breeding, Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
Plant Cell. 2023 Nov 30;35(12):4325-4346. doi: 10.1093/plcell/koad239.
CYP78A, a cytochrome P450 subfamily that includes rice (Oryza sativa L.) BIG GRAIN2 (BG2, CYP78A13) and Arabidopsis thaliana KLUH (KLU, CYP78A5), generate an unknown mobile growth signal (referred to as a CYP78A-derived signal) that increases grain (seed) size. However, the mechanism by which the CYP78A pathway increases grain size remains elusive. Here, we characterized a rice small grain mutant, small grain4 (smg4), with smaller grains than its wild type due to restricted cell expansion and cell proliferation in spikelet hulls. SMG4 encodes a multidrug and toxic compound extrusion (MATE) transporter. Loss of function of SMG4 causes smaller grains while overexpressing SMG4 results in larger grains. SMG4 is mainly localized to endoplasmic reticulum (ER) exit sites (ERESs) and partially localized to the ER and Golgi. Biochemically, SMG4 interacts with coat protein complex Ⅱ (COPⅡ) components (Sar1, Sec23, and Sec24) and CYP78As (BG2, GRAIN LENGTH 3.2 [GL3.2], and BG2-LIKE 1 [BG2L1]). Genetically, SMG4 acts, at least in part, in a common pathway with Sar1 and CYP78As to regulate grain size. In summary, our findings reveal a CYP78As-SMG4-COPⅡ regulatory pathway for grain size in rice, thus providing new insights into the molecular and genetic regulatory mechanism of grain size.
CYP78A 是细胞色素 P450 亚家族的一员，包括水稻（Oryza sativa L.）的 BIG GRAIN2（BG2，CYP78A13）和拟南芥（Arabidopsis thaliana）的 KLUH（KLU，CYP78A5），它们产生一种未知的可移动生长信号（称为 CYP78A 衍生信号），可增加谷物（种子）的大小。然而，CYP78A 途径增加谷物大小的机制仍然难以捉摸。在这里，我们表征了一个水稻小粒突变体 small grain4（smg4），由于小穗壳中的细胞扩张和细胞增殖受到限制，其籽粒比野生型小。SMG4 编码一种多药和毒性化合物外排（MATE）转运蛋白。SMG4 的功能丧失导致籽粒变小，而过表达 SMG4 则导致籽粒变大。SMG4 主要定位于内质网（ER）出口部位（ERES），部分定位于 ER 和高尔基体。从生化角度来看，SMG4 与衣壳蛋白复合物 Ⅱ（COPⅡ）成分（Sar1、Sec23 和 Sec24）和 CYP78As（BG2、GRAIN LENGTH 3.2 [GL3.2] 和 BG2-LIKE 1 [BG2L1]）相互作用。从遗传学角度来看，SMG4 至少部分与 Sar1 和 CYP78As 共同作用，调节籽粒大小。总之，我们的发现揭示了一个 CYP78As-SMG4-COPⅡ调控途径，用于调控水稻的籽粒大小，从而为籽粒大小的分子和遗传调控机制提供了新的见解。
