Carvalho Humberto H, Brustolini Otávio J B, Pimenta Maiana R, Mendes Giselle C, Gouveia Bianca C, Silva Priscila A, Silva José Cleydson F, Mota Clenilso S, Soares-Ramos Juliana R L, Fontes Elizabeth P B
National Institute of Science and Technology in Plant-Pest Interactions, Universidade Federal de Viçosa, Viçosa, MG, Brazil ; Departamento de Biologia Vegetal, Universidade Federal de Viçosa, Viçosa, MG, Brazil.
National Institute of Science and Technology in Plant-Pest Interactions, Universidade Federal de Viçosa, Viçosa, MG, Brazil ; Departamento de Bioquímica e Biologia Molecular/Bioagro, Universidade Federal de Viçosa, Viçosa, MG, Brazil.
PLoS One. 2014 Jan 29;9(1):e86661. doi: 10.1371/journal.pone.0086661. eCollection 2014.
BiP overexpression improves leaf water relations during droughts and delays drought-induced leaf senescence. However, whether BiP controls cellular homeostasis under drought conditions or simply delays dehydration-induced leaf senescence as the primary cause for water stress tolerance remains to be determined. To address this issue, we examined the drought-induced transcriptomes of BiP-overexpressing lines and wild-type (WT) lines under similar leaf water potential (ψw) values. In the WT leaves, a ψw reduction of -1.0 resulted in 1339 up-regulated and 2710 down-regulated genes; in the BiP-overexpressing line 35S::BiP-4, only 334 and 420 genes were induced and repressed, respectively, at a similar leaf ψw = -1.0 MPa. This level of leaf dehydration was low enough to induce a repertory of typical drought-responsive genes in WT leaves but not in 35S::BiP-4 dehydrated leaves. The responders included hormone-related genes, functional and regulatory genes involved in drought protection and senescence-associated genes. The number of differentially expressed genes in the 35S::BiP-4 line approached the wild type number at a leaf ψw = -1.6 MPa. However, N-rich protein (NRP)- mediated cell death signaling genes and unfolded protein response (UPR) genes were induced to a much lower extent in the 35S::BiP-4 line than in the WT even at ψw = -1.6 MPa. The heatmaps for UPR, ERAD (ER-associated degradation protein system), drought-responsive and cell death-associated genes revealed that the leaf transcriptome of 35S::BiP-4 at ψw = -1.0 MPa clustered together with the transcriptome of well-watered leaves and they diverged considerably from the drought-induced transcriptome of the WT (ψw = -1.0, -1.7 and -2.0 MPa) and 35S::BiP-4 leaves at ψw = -1.6 MPa. Taken together, our data revealed that BiP-overexpressing lines requires a much higher level of stress (ψw = -1.6 MPa) to respond to drought than that of WT (ψw = -1.0). Therefore, BiP overexpression maintains cellular homeostasis under water stress conditions and thus ameliorates endogenous osmotic stress.
BiP过表达可改善干旱期间的叶片水分关系并延缓干旱诱导的叶片衰老。然而，BiP是在干旱条件下控制细胞内稳态，还是仅仅作为水分胁迫耐受性的主要原因延缓脱水诱导的叶片衰老，仍有待确定。为了解决这个问题，我们检测了在相似叶片水势（ψw）值下BiP过表达株系和野生型（WT）株系的干旱诱导转录组。在WT叶片中，ψw降低-1.0导致1339个基因上调和2710个基因下调；在BiP过表达株系35S::BiP-4中，在相似的叶片ψw = -1.0 MPa时，分别只有334个和420个基因被诱导和抑制。这种程度的叶片脱水程度低到足以在WT叶片中诱导一系列典型的干旱响应基因，但在35S::BiP-4脱水叶片中则不然。这些响应基因包括激素相关基因、参与干旱保护的功能和调控基因以及衰老相关基因。在叶片ψw = -1.6 MPa时，35S::BiP-4株系中差异表达基因的数量接近野生型。然而，即使在ψw = -1.6 MPa时，35S::BiP-4株系中富氮蛋白（NRP）介导的细胞死亡信号基因和未折叠蛋白反应（UPR）基因的诱导程度也比WT低得多。UPR、内质网相关降解（ERAD，内质网相关降解蛋白系统）、干旱响应和细胞死亡相关基因的热图显示，ψw = -1.0 MPa时35S::BiP-4的叶片转录组与充分浇水叶片的转录组聚集在一起，并且它们与WT（ψw = -1.0、-1.7和-2.0 MPa）和ψw = -1.6 MPa时35S::BiP-4叶片的干旱诱导转录组有很大差异。综上所述，我们的数据表明，与WT（ψw = -1.0）相比，BiP过表达株系需要更高水平的胁迫（ψw = -1.6 MPa）来响应干旱。因此，BiP过表达在水分胁迫条件下维持细胞内稳态，从而减轻内源性渗透胁迫。
