Molecular Mechanism by Which the GATA Transcription Factor CcNsdD2 Regulates the Developmental Fate of <i>Coprinopsis cinerea</i> under Dark or Light Conditions

Abstract

Coprinopsis cinerea has seven homologs of the Aspergillus nidulans transcription factor NsdD. Of these, CcNsdD1 and CcNsdD2 from <i>C. cinerea</i> show the best identities of 62 and 50% to A. nidulans NsdD, respectively. After 4 days of constant darkness cultivation, <i>CcnsdD2</i>, but not <i>CcnsdD1</i>, was upregulated on the first day of light/dark cultivation to induce fruiting bodies, and overexpression of <i>CcnsdD2</i>, but not <i>CcnsdD1</i>, produced more fruiting bodies under a light/dark rhythm. Although single knockdown of <i>CcnsdD2</i> did not affect fruiting body production due to upregulation of its homolog <i>CcnsdD1</i>, the double-knockdown CcNsdD1/NsdD2-RNAi transformant showed defects in fruiting body formation under a light/dark rhythm. Knockdown of <i>CcnsdD1</i>/<i>nsdD2</i> led to the differentiation of primary hyphal knots into sclerotia rather than secondary hyphal knots under a light/dark rhythm, similar to the differentiation of primary hyphal knots into sclerotia of the wild-type strain under darkness. The CcNsdD2-overexpressing transformant produced more primary hyphal knots, secondary hyphal knots, and fruiting bodies under a light/dark rhythm but only more primary hyphal knots and sclerotia under darkness. RNA-seq revealed that some genes reported previously to be involved in formation of hyphal knots and primordia, cyclopropane-fatty-acyl-phospholipid synthases <i>cfs1-3</i>, galectins <i>cgl1-3</i>, and hydrophobins <i>hyd1-3</i> were downregulated in the CcNsdD1/NsdD2-RNAi transformant compared to the mock transformant. ChIP-seq and electrophoretic mobility shift assay demonstrated that CcNsdD2 bound to promoter regulatory sequences containing a GATC motif in <i>cfs1</i>, <i>cfs2</i>, <i>cgl1</i>, and <i>hyd1</i>. A molecular mechanism by which CcNsdD2 regulates the developmental fate of <i>C. cinerea</i> under dark or light conditions is proposed. <b>IMPORTANCE</b> The model mushroom Coprinopsis cinerea exhibits remarkable photomorphogenesis during fruiting body development. This study reports that the <i>C. cinerea</i> transcription factor CcNsdD2 promotes primary hyphal knot formation by upregulating <i>cfs1</i>, <i>cfs2</i>, <i>cgl1</i>, and <i>hyd1</i>. Although the induction of <i>CcnsdD2</i> is not under direct control of light and photoreceptors, the CcNsdD2-mediated developmental fates of the primary hyphal knots depend on the following light/dark rhythm cultivation or dark cultivation after full growth of mycelia in the constant dark cultivation. This study provides new insight into the molecular mechanism by which CcNsdD2 regulates the developmental fate of <i>C. cinerea</i> under dark or light conditions. In addition, the result that overexpression of <i>CcnsdD2</i> induced more secondary hyphal knots, primordia, and fruiting bodies under light/dark rhythm cultivation conditions has potential applied value in the edible mushroom industry.