CRYs possess a conserved photolyase-homologous region and a divergent C-terminal domain. The photolyase-homologous region binds flavin adenine dinucleotide, which is responsible for light activation. Blue-light-activated phosphorylation leads to a conformational change that exposes a short motif of 80 residues and enables dimerization. Dimerized light-activated CRYs are known to bind various target proteins to induce downstream responses, such as inhibition of hypocotyl elongation. By contrast, monomeric CRYs interact with some proteins in a light-independent way, which suggests that such interactions are not related to light signalling. Whether monomeric CRYs can also interact with proteins in a light-dependent way was not known.

To investigate this possibility, the researchers performed a screen for interactors of a mutated form of CRY2 that is unable to dimerize, and found that FORKED-LIKE 1 (FL1) and FL3 (FLs) interact with monomeric CRY2. In contrast to previously known interactors of monomeric CRY2, the interaction with FL1 and FL3 is inhibited by blue light. The fl mutants show blue-light-enhanced defects in root elongation that are due to reduced cell division. This phenotype is opposite to that of cry2 mutants, which have longer roots in the dark. Many differentially expressed genes in fl and cry2 mutants compared to wild type are genes related to cell division and are regulated in the opposite way in these mutants: FLs promote expression and CRY2 inhibits it. Consequently, the long-root phenotype of cry2 in the dark is suppressed in the fl background, which suggests that FLs act downstream of CRY2 in the regulation of cell division in roots. In sum, the data suggest that monomeric CRY2 interacts with FLs in the dark, which inhibits FL activity and leads to reduced cell division and root growth. Blue light, on the other hand, leads to dissociation of CRY2 from FLs, which enables them to promote cell division.

CRYs 具有一个保守的光解酶同源区域和一个不同的 C 端结构域。光裂解酶同源区域结合黄素腺嘌呤二核苷酸，黄素腺嘌呤二核苷酸负责光激活。蓝光激活磷酸化导致构象变化，暴露出 80 个残基的短基序并实现二聚化。已知二聚化光激活 CRY 可结合各种靶蛋白以诱导下游反应，例如抑制下胚轴伸长。相比之下，单体 CRY 以不依赖光的方式与某些蛋白质相互作用，这表明这种相互作用与光信号传导无关。单体 CRY 是否也能以光依赖性方式与蛋白质相互作用尚不清楚。

为了研究这种可能性，研究人员对无法二聚化的突变形式的 CRY2 的相互作用子进行了筛选，发现 FORKED-LIKE 1 （FL1） 和 FL3 （FLs） 与单体 CRY2 相互作用。与以前已知的单体 CRY2 相互作用子相比，与 FL1 和 FL3 的相互作用受到蓝光的抑制。fl 突变体显示由于细胞分裂减少而导致的根伸长蓝光增强缺陷。这种表型与 cry2 突变体的表型相反，后者在黑暗中具有较长的根。与野生型相比，fl 和 cry2 突变体中的许多差异表达基因是与细胞分裂相关的基因，并且在这些突变体中以相反的方式受到调节：FL 促进表达，而 CRY2 抑制表达。因此，黑暗中 cry2 的长根表型在 fl 背景中受到抑制，这表明 FLs 在 CRY2 下游调节根细胞分裂。总之，数据表明单体 CRY2 在黑暗中与 FL 相互作用，从而抑制 FL 活性并导致细胞分裂和根生长减少。另一方面，蓝光导致 CRY2 与 FL 解离，这使它们能够促进细胞分裂。